PerformanceMonitor: do not maintain a vector of frames in the monitor, single ExecutionContext memb…

third_party/WebKit/Source/core/frame/LocalFrame.cpp

Index: third_party/WebKit/Source/core/frame/LocalFrame.cpp
diff --git a/third_party/WebKit/Source/core/frame/LocalFrame.cpp b/third_party/WebKit/Source/core/frame/LocalFrame.cpp
index 562818bc489268d2705db002be931d20c22c1dc0..9c4e3b26771df22569c577a3ea58022137108a30 100644
--- a/third_party/WebKit/Source/core/frame/LocalFrame.cpp
+++ b/third_party/WebKit/Source/core/frame/LocalFrame.cpp
@@ -391,6 +391,9 @@ void LocalFrame::detach(FrameDetachType type) {
   // DCHECK(!m_isDetaching) here.
   m_isDetaching = true;
 
+  if (isLocalRoot())
+    m_performanceMonitor->shutdown();
+
   PluginScriptForbiddenScope forbidPluginDestructorScripting;
   m_loader.stopAllLoaders();
   // Don't allow any new child frames to load in this frame: attaching a new