[code coverage] Update documentation for code coverage

This CL updates the documentation for code coverage.

TBR=jbudorick@chromium.org

Bug: 974379
Change-Id: If9abde5ce40793a7a4d265703fb695126d8f0e56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663371
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671397}

build/android/docs/coverage.md

@@ -73,7 +73,7 @@ class files and runtime **.exec** files. Then we need to process them using the
   ```
 
 2. We can also generate JSON format report for
-   [coverage tool](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/code_coverage.md)
+   [coverage tool](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/testing/code_coverage.md)
    created by Chrome Ops - CATS team.
    In this case, we need to change `--format` to json, for example:
 

docs/README.md

@@ -170,6 +170,9 @@ used when committed.
 *   [IPC Fuzzer](testing/ipc_fuzzer.md) - Fuzz testing of Chromium IPC interfaces.
 *   [Running Chrome tests with AddressSanitizer (asan) and LeakSanitizer (lsan)](testing/linux_running_asan_tests.md) -
     Run Chrome tests with ASAN and LSAN builds to detect addressability issues and memory leaks.
+*   [Code Coverage](testing/code_coverage.md) - Code coverage for Chromium.
+*   [Code Coverage in Gerrit](testing/code_coverage_in_gerrit.md) - Per-CL code
+    coverage in Gerrit to assist code reviews.
 
 ### GPU-related docs
 *   [GPU Pixel Wrangling](gpu/pixel_wrangling.md) - Instructions for GPU

docs/clang_code_coverage_wrapper.md

@@ -73,7 +73,7 @@ please [file a bug].
 For questions and general discussions, please join [code-coverage group].
 
 [//build/toolchain/clang_code_coverage_wrapper.py]: ../build/toolchain/clang_code_coverage_wrapper.py
-[code_coverage.md]: code_coverage.md
+[code_coverage.md]: testing/code_coverage.md
 [//tools/code_coverage/coverage.py]: ../tools/code_coverage/coverage.py
 [file a bug]: https://bugs.chromium.org/p/chromium/issues/entry?components=Tools%3ECodeCoverage
 [code-coverage group]: https://groups.google.com/a/chromium.org/forum/#!forum/code-coverage

docs/code_coverage.md → docs/testing/code_coverage.md

@@ -47,14 +47,14 @@ There are two types of builder:
 
 CI Builder
 
-The Code-coverage CI Builders periodically build all the test targets and fuzzer
+The code coverage CI Builders periodically build all the test targets and fuzzer
 targets for a given platform and instrument all available source files. Then
 save the coverage data to a dedicated storage bucket.
 
 CQ Builder
 
 The code coverage CQ builders instrument only the files changed for a given CL.
-more information about per-cl coverage info in [this
+More information about per-cl coverage info in [this
 doc](code_coverage_in_gerrit.md).
 
 ### Coverage Service
@@ -75,34 +75,40 @@ It shows the full-code coverage reports with links to the builds that generated
 them, as well as per-directory and per-component aggregation, and can be drilled
 down to the single line of code level of detail.
 
-Refer tho the following screenshots, or this [18-second video
-tutorial](https://www.youtube.com/watch?v=eX7im2_3YfA).
-
-##### Project View
-
-![coverage dashboard main view]
+Refer to the following screenshots:
 
 ##### Directory View
 
+See coverage breakdown by directories (default landing page).
+
 ![coverage dashboard directory view]
 
 ##### Component View
 
+Use the view dropdown menu to switch between directory and component.
+
 ![coverage dashboard component view]
 
 ##### Source View
 
-When you click on a particular source file in one of the views above, you can check
-per-line coverage information such as
-
-- Uncovered / Covered line fragments, lines and code blocks. This information can be
-useful to identify areas of code that lack test coverage.
-- Per-line hit counts indicating how many times this line was hit by all tested targets.
-This information can be useful to determine hot spots in your code.
+Click on a particular source file in one of the views above to see line-by-line
+coverage breakdown, and it's useful to identify:
+- Uncovered lines and code blocks that lack test coverage.
 - Potentially dead code. See [dead code example].
+- Hot spots in your code.
 
 ![coverage dashboard file view]
 
+##### Project View
+
+Click on "Previous Reports" to check out the coverage history of the project.
+
+![coverage dashboard link to previous reports]
+
+List of historical coverage reports are in reverse chronological order.
+
+![coverage dashboard previous reports]
+
 #### Gerrit Coverage View
 
 The other client supported at the moment is the gerrit plugin for code coverage.
@@ -293,11 +299,6 @@ reported usually grows after that.
 
 ### How can I improve [coverage dashboard]?
 
-Source code of the dashboard is not open sourced at the moment, but if you are a
-Googler, you should have access to the code-coverage repository. There is a
-documentation and scripts for running it locally. To get access and report
-issues, ping the [code-coverage group].
-
 The code for the service and dashboard currently lives along with findit at
 [this location](https://chromium.googlesource.com/infra/infra/+/master/appengine/findit/)
 because of significant shared logic.
@@ -317,7 +318,8 @@ for that particular report (rightmost column on the [coverage dashboard]).
 If there is any failure, please upload a CL with the fix. If you can't fix it,
 feel free to [file a bug].
 * A particular test may not be available on a particular platform. As of now,
-only reports generated on Linux are available on the [coverage dashboard].
+only reports generated on Linux and CrOS are available on the
+[coverage dashboard].
 
 ### Is coverage reported for the code executed inside the sandbox?
 
@@ -336,7 +338,8 @@ information, see [crbug.com/842424].
 [coverage dashboard file view]: images/code_coverage_dashboard_file_view.png
 [coverage dashboard component view]: images/code_coverage_dashboard_component_view.png
 [coverage dashboard directory view]: images/code_coverage_dashboard_directory_view.png
-[coverage dashboard main view]: images/code_coverage_dashboard_main_view.png
+[coverage dashboard link to previous reports]: images/code_coverage_dashboard_link_to_previous_reports.png
+[coverage dashboard previous reports]: images/code_coverage_dashboard_previous_reports.png
 [crbug.com/821617]: https://crbug.com/821617
 [crbug.com/831939]: https://crbug.com/831939
 [crbug.com/834781]: https://crbug.com/834781
@@ -347,7 +350,7 @@ information, see [crbug.com/842424].
 [documentation]: https://clang.llvm.org/docs/SourceBasedCodeCoverage.html
 [file a bug]: https://bugs.chromium.org/p/chromium/issues/entry?components=Tools%3ECodeCoverage
 [file a new issue]: https://bugs.chromium.org/p/chromium/issues/entry?components=Tools%3ECodeCoverage
-[gerrit coverage view]: images/code_coverage_uncovered_lines.png
+[gerrit coverage view]: images/code_coverage_annotations.png
 [guide]: http://llvm.org/docs/CommandGuide/llvm-cov.html
 [How do crashes affect code coverage?]: #how-do-crashes-affect-code-coverage
 [known issues]: https://bugs.chromium.org/p/chromium/issues/list?q=component:Tools%3ECodeCoverage

tools/code_coverage/coverage.py

@@ -62,7 +62,7 @@
   For more options, please refer to tools/code_coverage/coverage.py -h.
 
   For an overview of how code coverage works in Chromium, please refer to
-  https://chromium.googlesource.com/chromium/src/+/master/docs/code_coverage.md
+  https://chromium.googlesource.com/chromium/src/+/master/docs/testing/code_coverage.md
 """
 
 from __future__ import print_function