Add support for tracing in browser tests.

content/public/common/content_switches.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/public/common/content_switches.h"
 
 #include "base/command_line.h"
 
 namespace switches {
 
@@ skipping 430 matching lines @@
 // Enable support for sync events in ServiceWorkers.
 const char kEnableServiceWorkerSync[]       = "enable-service-worker-sync";
 
 // Enable use of experimental TCP sockets API for sending data in the
 // SYN packet.
 const char kEnableTcpFastOpen[]             = "enable-tcp-fastopen";
 
 // Enabled threaded compositing for layout tests.
 const char kEnableThreadedCompositing[] = "enable-threaded-compositing";
 
+// Enable tracing during the execution of browser tests.
+const char kEnableTracing[] = "enable-tracing";

[jam, 2014/08/27 03:33:59]

nit: here and below, almost all flags have the '=' at the same column, please
follow that

+
+// 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[] =
     "enable-usermedia-screen-capturing";
 
 // Enables the use of the @viewport CSS rule, which allows
 // pages to control aspects of their own layout. This also turns on touch-screen
 // pinch gestures.
 const char kEnableViewport[]                = "enable-viewport";
 
 // Enables the use of the legacy viewport meta tag. Turning this on also
@@ skipping 454 matching lines @@
 // Enable the Win32K process mitigation policy for renderer processes which
 // prevents them from invoking user32 and gdi32 system calls which enter
 // the kernel. This is only supported on Windows 8 and beyond.
 const char kEnableWin32kRendererLockDown[]
     = "enable_win32k_renderer_lockdown";
 #endif
 
 // Don't dump stuff here, follow the same order as the header.
 
 }  // namespace switches