Add DevToolsAgent::{enable,disable}Tracing

content/renderer/devtools/devtools_agent.cc

Index: content/renderer/devtools/devtools_agent.cc
diff --git a/content/renderer/devtools/devtools_agent.cc b/content/renderer/devtools/devtools_agent.cc
index 3033733ba77323853f0ea83caee770789a64c27d..a2081248d6a5e5800a8fe837fcd9a31b3d797256 100644
--- a/content/renderer/devtools/devtools_agent.cc
+++ b/content/renderer/devtools/devtools_agent.cc
@@ -161,6 +161,17 @@ void DevToolsAgent::setTraceEventCallback(const WebString& category_filter,
   }
 }
 
+void DevToolsAgent::enableTracing(const WebString& category_filter) {
+  TraceLog* trace_log = TraceLog::GetInstance();
+  trace_log->SetEnabled(base::debug::CategoryFilter(category_filter.utf8()),
+                        TraceLog::RECORDING_MODE,
+                        TraceLog::RECORD_UNTIL_FULL);
+}
+
+void DevToolsAgent::disableTracing() {
+  TraceLog::GetInstance()->SetDisabled();
+}
+
 // static
 void DevToolsAgent::TraceEventCallbackWrapper(
     base::TimeTicks timestamp,