Remove ContextClient from DOMWindowPerformance

Now that DOMWindowPerformance can access DOMWindow with host(),
DOMWindowPerformance doesn't need to observe ContextClient.

This CL removes DOMWindowPerformance::m_window.

BUG=610176

Review-Url: https://codereview.chromium.org/2615633011
Cr-Commit-Position: refs/heads/master@{#441902}

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

@@ -11,13 +11,11 @@
 namespace blink {
 
 DOMWindowPerformance::DOMWindowPerformance(LocalDOMWindow& window)
-    : ContextClient(window.frame()), m_window(&window) {}
+    : Supplement<LocalDOMWindow>(window) {}
 
 DEFINE_TRACE(DOMWindowPerformance) {
-  visitor->trace(m_window);
   visitor->trace(m_performance);
   Supplement<LocalDOMWindow>::trace(visitor);
-  ContextClient::trace(visitor);
 }
 
 // static
@@ -43,7 +41,7 @@ Performance* DOMWindowPerformance::performance(DOMWindow& window) {
 
 Performance* DOMWindowPerformance::performance() {
   if (!m_performance)
-    m_performance = Performance::create(m_window->frame());
+    m_performance = Performance::create(host()->frame());
   return m_performance.get();
 }
 

third_party/WebKit/Source/core/timing/DOMWindowPerformance.h

@@ -6,7 +6,6 @@
 #define DOMWindowPerformance_h
 
 #include "core/CoreExport.h"
-#include "core/dom/ContextLifecycleObserver.h"
 #include "core/frame/LocalDOMWindow.h"
 #include "platform/Supplementable.h"
 #include "platform/heap/Handle.h"
@@ -15,13 +14,11 @@
 namespace blink {
 
 class DOMWindow;
-class LocalDOMWindow;
 class Performance;
 
 class CORE_EXPORT DOMWindowPerformance final
     : public GarbageCollected<DOMWindowPerformance>,
-      public Supplement<LocalDOMWindow>,
-      public ContextClient {
+      public Supplement<LocalDOMWindow> {
   USING_GARBAGE_COLLECTED_MIXIN(DOMWindowPerformance);
   WTF_MAKE_NONCOPYABLE(DOMWindowPerformance);
 
@@ -37,8 +34,6 @@ class CORE_EXPORT DOMWindowPerformance final
 
   Performance* performance();
 
-  // TODO(sof): try to move this direct reference and instead rely on frame().
-  Member<LocalDOMWindow> m_window;
   Member<Performance> m_performance;
 };