Remove performanceMonitor()->unsubscribeAll() from Performance's destructor

third_party/WebKit/Source/core/timing/Performance.cpp

Index: third_party/WebKit/Source/core/timing/Performance.cpp
diff --git a/third_party/WebKit/Source/core/timing/Performance.cpp b/third_party/WebKit/Source/core/timing/Performance.cpp
index abae0a17e72d92f137232a2230b0c36c2ba35712..5e513e6222e76e7e611f693fa199918c621d77f5 100644
--- a/third_party/WebKit/Source/core/timing/Performance.cpp
+++ b/third_party/WebKit/Source/core/timing/Performance.cpp
@@ -104,8 +104,9 @@ Performance::Performance(LocalFrame* frame)
       ContextLifecycleObserver(frame ? frame->document() : nullptr) {}
 
 Performance::~Performance() {
-  if (frame())
-    frame()->performanceMonitor()->unsubscribeAll(this);
+  // contextDestryoed() should have been called and the performance
+  // monitors should have been unsubscribed.
+  DCHECK(!frame());
 }
 
 void Performance::contextDestroyed() {