compositor-worker: Add CompositorProxyClient worker client of CompositorWorker.

third_party/WebKit/Source/web/ChromeClientImpl.cpp

Index: third_party/WebKit/Source/web/ChromeClientImpl.cpp
diff --git a/third_party/WebKit/Source/web/ChromeClientImpl.cpp b/third_party/WebKit/Source/web/ChromeClientImpl.cpp
index ab5b0e7b38da10ede99bb915ea7f6405b1e21267..64bd29b11e399eeacb524392bdf1c24450ff2e86 100644
--- a/third_party/WebKit/Source/web/ChromeClientImpl.cpp
+++ b/third_party/WebKit/Source/web/ChromeClientImpl.cpp
@@ -1073,6 +1073,12 @@ void ChromeClientImpl::didUpdateTopControls() const
     m_webView->didUpdateTopControls();
 }
 
+CompositorProxyClient* ChromeClientImpl::createCompositorProxyClient(LocalFrame* frame)
+{
+    WebLocalFrameImpl* webFrame = WebLocalFrameImpl::fromFrame(frame);
+    return webFrame->frameWidget()->createCompositorProxyClient();

[dcheng, 2016/05/20 23:57:47]

frameWidget() is only non-null on "local roots", so this probably needs to find
the local root first before trying to use the frame widget.

[flackr, 2016/05/25 17:47:40]

Done, but can you clarify something. If the root is not local, does that mean
the current frame is not running in this process? If that's the case, we should
probably return NULL with a TODO to actually create a compositor proxy client
instance on that frame. I'm not sure how we get into this circumstance though
when this is triggered from running "new CompositorWorker" in the frame we want
to create the worker for.

[kenrb, 2016/05/25 18:02:17]

A 'local root' is either the top-level frame, or a local frame that has a remote
frame parent. We introduced the local root concept because if a local frame is
an OOPIF then basically it acts like a top-level frame for its descendant frames
(e.g. it has a RenderWidget and a compositor). If there are no OOPIFs on a page
then only the top-level frame has a non-null frameWidget(), but in an OOPIF
process you need to get it from the local root.

I think the code (before the most recent change) would crash if you created a
compositor worker in a local subframe?

+}
+
 void ChromeClientImpl::registerPopupOpeningObserver(PopupOpeningObserver* observer)
 {
     DCHECK(observer);