v8binding: Initializes WindowProxy iff it's uninitialized.

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

Index: third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
index 5b012aaf1a0dc628afc0646d9bd629844ccc74de..64c5c75ca717b25562bada610bd7cf2a4e291edb 100644
--- a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
+++ b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
@@ -42,7 +42,6 @@ namespace blink {
 
 class DOMWindow;
 class Frame;
-class ScriptController;
 
 // WindowProxy implements the split window model of a window for a frame. In the
 // HTML standard, the split window model is composed of the Window interface
@@ -163,16 +162,60 @@ class WindowProxy : public GarbageCollectedFinalized<WindowProxy> {
   virtual bool isLocal() const { return false; }
 
  protected:
-  // TODO(dcheng): Remove this friend declaration once LocalWindowProxyManager
-  // and ScriptController are merged.
-  friend class ScriptController;
-
-  // A valid transition is from ContextUninitialized to ContextInitialized,
-  // and then ContextDetached. Other transitions are forbidden.
+  // Lifecycle represents the following four states.
+  //
+  // * ContextIsUninitialized
+  // We lazily initialize WindowProxies for performance reasons, and this state
+  // is "to be initialized on demand". WindowProxy basically behaves the same as
+  // |ContextIsInitialized| from a point of view of call sites.
+  // - Possible next states: ContextIsInitialized
+  // It's possible to detach the context's frame from the DOM or navigate to a
+  // new page without initializing the WindowProxy, however, there is no
+  // transition to |FrameIsDetached| or |GlobalObjectIsDetached|
+  // because |disposeContext| does not change the state if the state is
+  // |ContextIsUninitialized|. In either case of a) the browsing context
+  // container is detached from the DOM or b) the page is navigated away, there
+  // must be no way for author script to access the context of
+  // |ContextIsUninitialized| because |ContextIsUninitialized| means that author
+  // script has never accessed the context, hence there must exist no reference
+  // to the context.
+  //
+  // * ContextIsInitialized
+  // The context is initialized and its frame is still attached to the DOM.
+  // - Possible next states: FrameIsDetached, GlobalObjectIsDetached
+  //
+  // * GlobalObjectIsDetached
+  // The context is initialized and its frame is still attached to the DOM, and
+  // the page is now navigated away. The global object (inner global) is

[dcheng, 2017/03/30 21:03:01]

Maybe something like this would be slightly clearer:

The context is initialized and its frame is still attached to the DOM,
but the inner global's Document is no longer the active Document of the
frame (i.e. it is being navigated away).

[Yuki, 2017/03/31 07:32:09]

Done.

+  // detached from the global proxy (outer global), but the (detached) global
+  // object and context are still alive, and author script may have references
+  // to the context.
+  // The spec does not support full web features in this state. Blink supports
+  // less things than the spec.
+  // - Possible next states: ContextIsInitialized
+  // This state is in the middle of navigation. Once document loading is
+  // completed, the WindowProxy will always be reinitialized, as
+  // |DocumentLoader::installNewDocument| ends up calling to
+  // |WindowProxy::updateDocument|, which reinitializes the WindowProxy.
+  //
+  // * FrameIsDetached
+  // The context was initialized, but its frame has been detached from the DOM.
+  // Note that the context is still alive and author script may have references
+  // to the context and hence author script may run in the context.
+  // The spec does not support some of web features such as setTimeout, etc. on
+  // a detached window. Blink supports less things than the spec.
+  // V8PerContextData is cut off from the context.
+  // - Possible next states: n/a
   enum class Lifecycle {
-    ContextUninitialized,
-    ContextInitialized,
-    ContextDetached,
+    // v8::Context is not yet initialized.
+    ContextIsUninitialized,
+    // v8::Context is initialized.
+    ContextIsInitialized,
+    // The global object (inner global) is detached from the global proxy (outer
+    // global).
+    GlobalObjectIsDetached,
+    // The context's frame is detached from the DOM.
+    FrameIsDetached,
   };
 
   WindowProxy(v8::Isolate*, Frame&, RefPtr<DOMWrapperWorld>);