Add a mode flag to the tracing framework.

content/browser/devtools/devtools_tracing_handler.cc

Index: content/browser/devtools/devtools_tracing_handler.cc
diff --git a/content/browser/devtools/devtools_tracing_handler.cc b/content/browser/devtools/devtools_tracing_handler.cc
index e16768f6dc8c8b2ad00a9c11e5414969fb965c2b..20b397d737628d8cbf2d7fb0ddf766871562887e 100644
--- a/content/browser/devtools/devtools_tracing_handler.cc
+++ b/content/browser/devtools/devtools_tracing_handler.cc
@@ -26,6 +26,7 @@ const char kTracingCompleteNotification[] = "Tracing.tracingComplete";
 const char kTracingDataCollected[] = "Tracing.dataCollected";
 
 const char kCategoriesParam[] = "categories";
+const char kTraceModeParam[] = "trace-mode";
 
 }  // namespace
 
@@ -63,7 +64,15 @@ DevToolsTracingHandler::OnStart(DevToolsProtocol::Command* command) {
   base::DictionaryValue* params = command->params();
   if (params && params->HasKey(kCategoriesParam))
     params->GetString(kCategoriesParam, &categories);
-  TraceController::GetInstance()->BeginTracing(this, categories);
+
+  base::debug::TraceLog::TraceMode mode = base::debug::TraceLog::UNTIL_FULL;
+  if (params && params->HasKey(kTraceModeParam)) {
+    std::string mode_param;
+    params->GetString(kTraceModeParam, &mode_param);
+    mode = base::debug::TraceLog::TraceModeFromString(mode_param);
+  }
+
+  TraceController::GetInstance()->BeginTracing(this, categories, mode);
   is_running_ = true;
   return command->SuccessResponse(NULL);
 }