Submit CompositorFrame from worker

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

Index: third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
diff --git a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
index cbf5eda9b95dbc736a508dd338ccd244716aa4bc..200d0ba317fc6a5655325e01f63532bc247c3607 100644
--- a/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
+++ b/third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp
@@ -145,8 +145,12 @@ bool OffscreenCanvas::isPaintable() const
 
 OffscreenCanvasFrameDispatcher* OffscreenCanvas::getOrCreateFrameDispatcher()
 {
-    if (!m_frameDispatcher)
+    if (!m_frameDispatcher) {
+        // The frame dispatcher connects the current thread of OffscreenCanvas
+        // (either main or worker) to the browser process and remains unchanged
+        // throughout the lifetime of this OffscreenCanvas.
         m_frameDispatcher = wrapUnique(new OffscreenCanvasFrameDispatcherImpl(m_clientId, m_localId, m_nonce, width(), height()));
+    }
     return m_frameDispatcher.get();
 }