Add support for tracing in browser tests.

This CL adds support for collecting tracing data during the execution of browser tests. It is currently not possible to do so, yet it is very useful to be able to collect this data and analyze it without having to step through with debugger.

BUG=

Review URL: https://codereview.chromium.org/506113002

Cr-Commit-Position: refs/heads/master@{#292156}

content/public/common/content_switches.cc

@@ -447,7 +447,13 @@ const char kEnableServiceWorkerSync[]       = "enable-service-worker-sync";
 const char kEnableTcpFastOpen[]             = "enable-tcp-fastopen";
 
 // Enabled threaded compositing for layout tests.
-const char kEnableThreadedCompositing[] = "enable-threaded-compositing";
+const char kEnableThreadedCompositing[]     = "enable-threaded-compositing";
+
+// Enable tracing during the execution of browser tests.
+const char kEnableTracing[]                 = "enable-tracing";
+
+// The filename to write the output of the test tracing to.
+const char kEnableTracingOutput[]           = "enable-tracing-output";
 
 // Enable screen capturing support for MediaStream API.
 const char kEnableUserMediaScreenCapturing[] =

content/public/common/content_switches.h

@@ -132,6 +132,8 @@ CONTENT_EXPORT extern const char kEnableServiceWorkerSync[];
 CONTENT_EXPORT extern const char kEnableTargetedStyleRecalc[];
 CONTENT_EXPORT extern const char kEnableTcpFastOpen[];
 CONTENT_EXPORT extern const char kEnableThreadedCompositing[];
+CONTENT_EXPORT extern const char kEnableTracing[];
+CONTENT_EXPORT extern const char kEnableTracingOutput[];
 CONTENT_EXPORT extern const char kEnableUserMediaScreenCapturing[];
 CONTENT_EXPORT extern const char kEnableViewport[];
 CONTENT_EXPORT extern const char kEnableViewportMeta[];

content/public/test/browser_test_base.cc

@@ -15,6 +15,7 @@
 #include "content/public/app/content_main.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/browser/tracing_controller.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/main_function_params.h"
 #include "content/public/test/test_launcher.h"
@@ -121,6 +122,12 @@ class LocalHostResolverProc : public net::HostResolverProc {
   virtual ~LocalHostResolverProc() {}
 };
 
+void TraceDisableRecordingComplete(const base::Closure& quit,
+                                   const base::FilePath& file_path) {
+  LOG(ERROR) << "Tracing written to: " << file_path.value();
+  quit.Run();
+}
+
 }  // namespace
 
 extern int BrowserMain(const MainFunctionParams&);
@@ -269,7 +276,35 @@ void BrowserTestBase::ProxyRunTestOnMainThreadLoop() {
     signal(SIGTERM, DumpStackTraceSignalHandler);
   }
 #endif  // defined(OS_POSIX)
+
+  if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kEnableTracing)) {
+    base::debug::CategoryFilter category_filter(
+        CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+            switches::kEnableTracing));
+    TracingController::GetInstance()->EnableRecording(
+        category_filter,
+        base::debug::TraceOptions(base::debug::RECORD_CONTINUOUSLY),
+        TracingController::EnableRecordingDoneCallback());
+  }
+
   RunTestOnMainThreadLoop();
+
+  if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kEnableTracing)) {
+    base::FilePath trace_file =
+        CommandLine::ForCurrentProcess()->GetSwitchValuePath(
+            switches::kEnableTracingOutput);
+    // If there was no file specified, put a hardcoded one in the current
+    // working directory.
+    if (trace_file.empty())
+      trace_file = base::FilePath().AppendASCII("trace.json");
+
+    // Wait for tracing to collect results from the renderers.
+    base::RunLoop run_loop;
+    TracingController::GetInstance()->DisableRecording(
+        trace_file,
+        base::Bind(&TraceDisableRecordingComplete, run_loop.QuitClosure()));
+    run_loop.Run();
+  }
 }
 
 void BrowserTestBase::CreateTestServer(const base::FilePath& test_server_base) {