[Startup Tracing] Add --trace-config-file flag

content/app/android/library_loader_hooks.cc

Index: content/app/android/library_loader_hooks.cc
diff --git a/content/app/android/library_loader_hooks.cc b/content/app/android/library_loader_hooks.cc
index 39ef2b08f73a21e3fd0be44b3c958c4dbe0a488c..2a1a3dfd72a476bca7082b47d97dcd16f99891b2 100644
--- a/content/app/android/library_loader_hooks.cc
+++ b/content/app/android/library_loader_hooks.cc
@@ -16,7 +16,7 @@
 #include "base/strings/string_util.h"
 #include "base/trace_event/trace_event.h"
 #include "base/tracked_objects.h"
-#include "components/tracing/startup_tracing.h"
+#include "components/tracing/trace_config_file.h"
 #include "components/tracing/tracing_switches.h"
 #include "content/app/android/app_jni_registrar.h"
 #include "content/browser/android/browser_jni_registrar.h"
@@ -94,7 +94,11 @@ bool LibraryLoaded(JNIEnv* env, jclass clazz) {
     base::trace_event::TraceLog::GetInstance()->SetEnabled(
         trace_config, base::trace_event::TraceLog::RECORDING_MODE);
   } else {
-    tracing::EnableStartupTracingIfConfigFileExists();
+    if (tracing::TraceConfigFile::GetInstance()->IsEnabled()) {

[msw, 2015/08/25 18:06:49]

Maybe keep a helper like tracing::EnableStartupTracingIfConfigFileExists()?

[Zhen Wang, 2015/08/25 18:18:37]

TraceConfigFile is now more than just startup tracing. It also supports shutdown
tracing or stopping tracing via devtools (without startup duration). I think
using this format does not give the impression that this is only tied to startup
tracing.

[msw, 2015/08/25 18:22:46]

Fair enough.

+      base::trace_event::TraceLog::GetInstance()->SetEnabled(
+          tracing::TraceConfigFile::GetInstance()->GetTraceConfig(),
+          base::trace_event::TraceLog::RECORDING_MODE);
+    }
   }
 
   // Android's main browser loop is custom so we set the browser