Notify the Blink client synchronously if the initial doc is accessed.

third_party/WebKit/Source/core/loader/FrameLoaderClient.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 106 matching lines @@
     virtual void didStartLoading(LoadStartType) = 0;
     virtual void progressEstimateChanged(double progressEstimate) = 0;
     virtual void didStopLoading() = 0;
 
     virtual void loadURLExternally(const ResourceRequest&, NavigationPolicy, const String& suggestedName, bool replacesCurrentHistoryItem) = 0;
 
     virtual bool navigateBackForward(int offset) const = 0;
 
     // Another page has accessed the initial empty document of this frame.
     // It is no longer safe to display a provisional URL, since a URL spoof
-    // is now possible.
+    // is now possible.  The client must not call back into JavaScript during
+    // this notification.

[dcheng, 2016/07/22 06:22:03]

It makes me sad that this comment is necessary, since it really should be the
default for most callbacks. I'm honestly OK not having it at all actually, since
ScriptForbiddenScope will explode even in release mode. Similar thought for the
comment in WebFrameClient.

[Charlie Reis, 2016/07/22 16:41:44]

Yeah, I added it before we had the ScriptForbiddenScope, and I didn't have time
to revisit it last night when kicking off the try jobs for the new approach. 
I've removed them.

     virtual void didAccessInitialDocument() { }

[dglazkov, 2016/07/22 14:32:10]

The only user of this is RenderFrameImpl::didAccessInitialDocument, right? I
hope we're not planning to add overrides to this function.

[Charlie Reis, 2016/07/22 16:41:43]

That's right.  That's the only use, and there's no plans to add any more.

 
     // This frame has displayed inactive content (such as an image) from an
     // insecure source.  Inactive content cannot spread to other frames.
     virtual void didDisplayInsecureContent() = 0;
 
     // The indicated security origin has run active content (such as a
     // script) from an insecure source.  Note that the insecure content can
     // spread to other frames in the same origin.
     virtual void didRunInsecureContent(SecurityOrigin*, const KURL&) = 0;
     virtual void didDetectXSS(const KURL&, bool didBlockEntirePage) = 0;
@@ skipping 131 matching lines @@
 
     virtual LinkResource* createServiceWorkerLinkResource(HTMLLinkElement*) { return nullptr; }
 
     // Effective connection type when this frame was loaded.
     virtual WebEffectiveConnectionType getEffectiveConnectionType() { return WebEffectiveConnectionType::TypeUnknown; }
 };
 
 } // namespace blink
 
 #endif // FrameLoaderClient_h