Oilpan: Ensure that left-most vtable is the first thing to be initialized for...

Oilpan: Ensure that left-most vtable is the first thing to be initialized for polymorphic classes with trace methods.
    
This is done by ensuring one of two properties for any polymorphic class with a trace method.
1. If the trace method is virtual, then the left-most base class must define a virtual trace method too.
2. If the trace method is non-virtual, then the left-most base class must define some virtual method.
    
The Blink GC plugin statically checks these properties.

Review URL: https://codereview.chromium.org/463543002

git-svn-id: svn://svn.chromium.org/blink/trunk@180281 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/dom/Document.cpp

@@ -5787,6 +5787,7 @@ void Document::trace(Visitor* visitor)
     TreeScope::trace(visitor);
     ContainerNode::trace(visitor);
     ExecutionContext::trace(visitor);
+    LifecycleContext<Document>::trace(visitor);
 }
 
 } // namespace blink

third_party/WebKit/Source/core/dom/Document.h

@@ -204,7 +204,7 @@ public:
     void setObservedDocument(Document&);
 
 protected:
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
 
 private:
     void registerObserver(Document&);

third_party/WebKit/Source/core/dom/ExecutionContext.cpp

@@ -329,6 +329,7 @@ void ExecutionContext::trace(Visitor* visitor)
     visitor->trace(m_pendingExceptions);
 #endif
     WillBeHeapSupplementable<ExecutionContext>::trace(visitor);
+    LifecycleContext<ExecutionContext>::trace(visitor);
 }
 
 } // namespace blink

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

@@ -1917,6 +1917,7 @@ void LocalDOMWindow::trace(Visitor* visitor)
     visitor->trace(m_eventQueue);
     WillBeHeapSupplementable<LocalDOMWindow>::trace(visitor);
     EventTargetWithInlineData::trace(visitor);
+    LifecycleContext<LocalDOMWindow>::trace(visitor);
 }
 
 } // namespace blink

third_party/WebKit/Source/core/html/FormAssociatedElement.h

@@ -94,7 +94,7 @@ public:
 protected:
     FormAssociatedElement();
 
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
     void insertedInto(ContainerNode*);
     void removedFrom(ContainerNode*);
     void didMoveToNewDocument(Document& oldDocument);

third_party/WebKit/Source/core/page/Page.cpp

@@ -596,6 +596,7 @@ void Page::trace(Visitor* visitor)
     visitor->trace(m_frameHost);
 #endif
     WillBeHeapSupplementable<Page>::trace(visitor);
+    LifecycleContext<Page>::trace(visitor);
 }
 
 void Page::willBeDestroyed()

third_party/WebKit/Source/core/workers/AbstractWorker.h

@@ -58,6 +58,11 @@ public:
     AbstractWorker(ExecutionContext*);
     virtual ~AbstractWorker();
 
+    virtual void trace(Visitor* visitor)
+    {
+        EventTargetWithInlineData::trace(visitor);
+    }
+
 protected:
     // Helper function that converts a URL to an absolute URL and checks the result for validity.
     KURL resolveURL(const String& url, ExceptionState&);

third_party/WebKit/Source/modules/indexeddb/IndexedDBClient.h

@@ -38,7 +38,7 @@ class ExecutionContext;
 class IndexedDBClient : public GarbageCollected<IndexedDBClient> {
 public:
     static IndexedDBClient* create();
-    void trace(Visitor*) { }
+    virtual void trace(Visitor*) { }
 
     virtual bool allowIndexedDB(ExecutionContext*, const String& name) = 0;
 };

third_party/WebKit/Source/platform/LifecycleContext.h

@@ -36,6 +36,8 @@
 
 namespace blink {
 
+class Visitor;
+
 template <typename T>
 class LifecycleContext {
 public:
@@ -53,6 +55,8 @@ public:
     // Called from the destructor of observers.
     void wasUnobservedBy(Observer*);
 
+    virtual void trace(Visitor*) { }
+
 protected:
     Notifier& lifecycleNotifier();
 

third_party/WebKit/Source/platform/Supplementable.h

@@ -119,6 +119,7 @@ template<>
 class SupplementTracing<false> {
 public:
     virtual ~SupplementTracing() { }
+    virtual void trace(Visitor*) { }
 };
 
 template<typename T, bool isGarbageCollected = false>
@@ -143,26 +144,16 @@ public:
         return host ? host->requireSupplement(key) : 0;
     }
 
-    virtual void trace(Visitor*) { }
     virtual void willBeDestroyed() { }
 
     // FIXME: Oilpan: Remove this callback once PersistentHeapSupplementable is removed again.
     virtual void persistentHostHasBeenDestroyed() { }
 };
 
-template<typename T, bool>
-class SupplementableTracing;
-
-template<typename T>
-class SupplementableTracing<T, true> { };
-
-template<typename T>
-class SupplementableTracing<T, false> { };
-
 // Helper class for implementing Supplementable, HeapSupplementable, and
 // PersistentHeapSupplementable.
 template<typename T, bool isGarbageCollected = false>
-class SupplementableBase : public SupplementableTracing<T, isGarbageCollected> {
+class SupplementableBase {
 public:
     void provideSupplement(const char* key, typename SupplementableTraits<T, isGarbageCollected>::SupplementArgumentType supplement)
     {