Make V8IntersectionObserverDelegate inherit from ContextClient

We should use ContextClient instead of storing ScriptState because
ContextClient can check whether the context is destroyed.

Bug: 785553
Change-Id: Icf85fb6c3f97c9a50f85de812b812999669b96f5
Reviewed-on: https://chromium-review.googlesource.com/776136Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517318}

third_party/WebKit/Source/bindings/core/v8/V8IntersectionObserverDelegate.cpp

@@ -17,7 +17,8 @@ namespace blink {
 V8IntersectionObserverDelegate::V8IntersectionObserverDelegate(
     V8IntersectionObserverCallback* callback,
     ScriptState* script_state)
-    : callback_(callback), script_state_(script_state) {}
+    : ContextClient(ExecutionContext::From(script_state)),
+      callback_(callback) {}
 
 V8IntersectionObserverDelegate::~V8IntersectionObserverDelegate() {}
 
@@ -27,9 +28,14 @@ void V8IntersectionObserverDelegate::Deliver(
   callback_->call(&observer, entries, &observer);
 }
 
+ExecutionContext* V8IntersectionObserverDelegate::GetExecutionContext() const {
+  return ContextClient::GetExecutionContext();
+}
+
 void V8IntersectionObserverDelegate::Trace(blink::Visitor* visitor) {
   visitor->Trace(callback_);
   IntersectionObserverDelegate::Trace(visitor);
+  ContextClient::Trace(visitor);
 }
 
 void V8IntersectionObserverDelegate::TraceWrappers(

third_party/WebKit/Source/bindings/core/v8/V8IntersectionObserverDelegate.h

@@ -6,6 +6,7 @@
 #define V8IntersectionObserverDelegate_h
 
 #include "core/CoreExport.h"
+#include "core/dom/ContextLifecycleObserver.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/intersection_observer/IntersectionObserverDelegate.h"
 #include "platform/bindings/DOMWrapperWorld.h"
@@ -17,26 +18,25 @@ namespace blink {
 class V8IntersectionObserverCallback;
 
 class V8IntersectionObserverDelegate final
-    : public IntersectionObserverDelegate {
+    : public IntersectionObserverDelegate,
+      public ContextClient {
+  USING_GARBAGE_COLLECTED_MIXIN(V8IntersectionObserverDelegate);
+
  public:
   CORE_EXPORT V8IntersectionObserverDelegate(V8IntersectionObserverCallback*,
                                              ScriptState*);
   ~V8IntersectionObserverDelegate() override;
 
+  ExecutionContext* GetExecutionContext() const override;
+
   virtual void Trace(blink::Visitor*);
   virtual void TraceWrappers(const ScriptWrappableVisitor*) const;
 
   void Deliver(const HeapVector<Member<IntersectionObserverEntry>>&,
                IntersectionObserver&) override;
 
-  ExecutionContext* GetExecutionContext() const override {
-    return ExecutionContext::From(script_state_.get());
-  }
-
  private:
   TraceWrapperMember<V8IntersectionObserverCallback> callback_;
-  // TODO(bashi): Use ContextClient rather than holding ScriptState.
-  scoped_refptr<ScriptState> script_state_;
 };
 
 }  // namespace blink

third_party/WebKit/Source/core/intersection_observer/IntersectionObserver.cpp

@@ -329,6 +329,7 @@ String IntersectionObserver::rootMargin() const {
 
 void IntersectionObserver::EnqueueIntersectionObserverEntry(
     IntersectionObserverEntry& entry) {
+  DCHECK(delegate_->GetExecutionContext());
   entries_.push_back(&entry);
   ToDocument(delegate_->GetExecutionContext())
       ->EnsureIntersectionObserverController()