Move enable_paint_preview flag to //build/config.

This cl removes the following dependency:
 //third_party/harfbuzz-gn (1) -> //components/paint_preview (2)
Because for legacy reasons, (1) is rolled into WebRTC
whereas for good reason (2) isn't.

It will unblock chromium->WebRTC roll:
https://webrtc-review.googlesource.com/c/src/+/162503/
currently failing with:

ERROR at //third_party/harfbuzz-ng/BUILD.gn:9:1: Can't load input file.
import("//components/paint_preview/buildflags/buildflags.gni")

Bug: webrtc:11223, chromium:1031164
Change-Id: I67c75b3fc4cd8fa3daf93867f13209f785e7adf5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1978741
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Yves Gerey <yvesg@google.com>
Cr-Commit-Position: refs/heads/master@{#726954}

components/paint_preview/buildflags/buildflags.gni → build/config/buildflags_paint_preview.gni

@@ -9,6 +9,10 @@ declare_args() {
   # Enable basic paint preview support. Does not work on iOS or Fuchsia. Should
   # not be included with Chromecast. Not ready for shipping builds yet so
   # include in unofficial builds.
+  # Used by //components/paint_preview and //third_party/harfbuzz-ng.
+  # TODO(bug/webrtc:11223) Move back this file in //components/paint_preview/
+  #     once WebRTC doesn't roll harfbuzz-ng anymore, for consistency sake.
+  #     (Just revert the CL)
   enable_paint_preview =
       !is_chromecast && !is_ios && !is_fuchsia && !is_official_build
 }

chrome/renderer/BUILD.gn

@@ -2,12 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/buildflags_paint_preview.gni")
 import("//build/config/features.gni")
 import("//build/config/jumbo.gni")
 import("//chrome/common/features.gni")
 import("//components/nacl/features.gni")
 import("//components/offline_pages/buildflags/features.gni")
-import("//components/paint_preview/buildflags/buildflags.gni")
 import("//components/spellcheck/spellcheck_build_features.gni")
 import("//extensions/buildflags/buildflags.gni")
 import("//media/media_options.gni")

chrome/test/BUILD.gn

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/allocator.gni")
+import("//build/config/buildflags_paint_preview.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
@@ -22,7 +23,6 @@ import("//components/gwp_asan/buildflags/buildflags.gni")
 import("//components/nacl/features.gni")
 import("//components/offline_pages/buildflags/features.gni")
 import("//components/os_crypt/features.gni")
-import("//components/paint_preview/buildflags/buildflags.gni")
 import("//components/signin/features.gni")
 import("//components/spellcheck/spellcheck_build_features.gni")
 import("//extensions/buildflags/buildflags.gni")

components/paint_preview/buildflags/BUILD.gn

@@ -3,7 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/buildflag_header.gni")
-import("//components/paint_preview/buildflags/buildflags.gni")
+import("//build/config/buildflags_paint_preview.gni")
 
 # This target is standalone so any targets in the build can refer to the
 # buildflag without bringing in any paint preview targets.

third_party/harfbuzz-ng/BUILD.gn

@@ -2,11 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/buildflags_paint_preview.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/features.gni")
 import("//build/config/freetype/freetype.gni")
 import("//build/config/ui.gni")
-import("//components/paint_preview/buildflags/buildflags.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//third_party/harfbuzz-ng/harfbuzz.gni")