[Fuchsia] Fix flake in WebEngineDebugIntegrationTest

Each WebEngine integration test starts its own instance of WebEngine,
but WebEngineDebugIntegrationTests were assuming that there is only one
WebEngine instance running, so they were failing in some cases,
particularly after new tests were added. Fixed
WebEngineDebugIntegrationTest to handle the case when there are more
than one WebEngine. Now WebEngine is started with an argument that
allows it to distinguish different WebEngine instances.

Bug: 955589
Change-Id: I768197db05c694bbb6593f8d1e003a2897ef7cc6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2101244
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: David Dorwin <ddorwin@chromium.org>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749930}

fuchsia/engine/web_engine_debug_integration_test.cc

@@ -61,22 +61,48 @@ class WebEngineDebugIntegrationTest : public testing::Test {
   ~WebEngineDebugIntegrationTest() override = default;
 
   void SetUp() override {
-    web_context_provider_ =
-        cr_fuchsia::ConnectContextProvider(web_engine_controller_.NewRequest());
+    // Add an argument to WebEngine instance to distinguish it from other
+    // instances that may be started by other tests.
+    std::string test_arg =
+        std::string("--test-name=") +
+        testing::UnitTest::GetInstance()->current_test_info()->name();
+
+    base::CommandLine command_line(base::CommandLine::NO_PROGRAM);
+    command_line.AppendSwitch(test_arg);
+
+    web_context_provider_ = cr_fuchsia::ConnectContextProvider(
+        web_engine_controller_.NewRequest(), command_line);
     web_context_provider_.set_error_handler(
         [](zx_status_t status) { ADD_FAILURE(); });
 
     WaitForWebEngine();
 
-    // Connect to the Debug API.
+    // Enumerate all entries in /hub/c/context_provider.cmx to find WebEngine
+    // instance with |test_arg|.
     base::FileEnumerator file_enum(
         base::FilePath("/hub/c/context_provider.cmx"), false,
         base::FileEnumerator::DIRECTORIES);
-    web_engine_path_ = file_enum.Next();
-    ASSERT_FALSE(web_engine_path_.empty());
 
-    // There should only be one instance of WebEngine in the realm.
-    ASSERT_TRUE(file_enum.Next().empty());
+    for (auto dir = file_enum.Next(); !dir.empty(); dir = file_enum.Next()) {
+      std::string args;
+      if (!base::ReadFileToString(dir.Append("args"), &args)) {
+        // WebEngine may shutdown while we are enumerating the directory, so
+        // it's safe to ignore this error.
+        continue;
+      }
+
+      if (args.find(test_arg) != std::string::npos) {
+        // There should only one instance of WebEngine with |test_arg|.
+        EXPECT_TRUE(web_engine_path_.empty());
+
+        web_engine_path_ = dir;
+
+        // Keep iterating to check that there are no other matching instances.
+      }
+    }
+
+    // Check that we've found the WebEngine instance with |test_arg|.
+    ASSERT_FALSE(web_engine_path_.empty());
 
     debug_dir_ = std::make_unique<sys::ServiceDirectory>(
         base::fuchsia::OpenDirectory(web_engine_path_.Append("out/debug")));