Preparation for enabling slimming paint synchronized painting

third_party/WebKit/Source/web/WebGraphicsContextImpl.h

Index: third_party/WebKit/Source/web/WebGraphicsContextImpl.h
diff --git a/third_party/WebKit/Source/web/WebGraphicsContextImpl.h b/third_party/WebKit/Source/web/WebGraphicsContextImpl.h
index 954107656cc8dc6165d4e122bd09583e2697328b..0e1a9e464640c99812772aa3cedac9a1b8e5896e 100644
--- a/third_party/WebKit/Source/web/WebGraphicsContextImpl.h
+++ b/third_party/WebKit/Source/web/WebGraphicsContextImpl.h
@@ -6,6 +6,7 @@
 #define WebGraphicsContextImpl_h
 
 #include "platform/graphics/paint/DisplayItem.h"
+#include "platform/graphics/paint/DisplayItemCacheSkipper.h"
 #include "platform/graphics/paint/DisplayItemClient.h"
 #include "public/web/WebGraphicsContext.h"
 #include "wtf/OwnPtr.h"
@@ -33,6 +34,7 @@ private:
     DisplayItemClientWrapper m_client;
     DisplayItem::Type m_type;
     OwnPtr<DrawingRecorder> m_drawingRecorder;
+    DisplayItemCacheSkipper m_cacheSkipper;

[pdr., 2015/10/29 04:06:10]

I wouldn't expect WebGraphicsContext to disable caching. Is this just for
PageOverlay? If so, can we explicitly disable caching in PageOverlay?

[Xianzhu, 2015/10/29 04:22:01]

WebGraphicsContext seems to expect that no cache exists (in
WebGraphicsContextImpl::beginDrawing():
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...)

I encountered assertion failure in WebGraphicsContextImpl::beginDrawing().

Should we change beginDrawing() to allow caching? 

[chrishtr, 2015/10/29 20:22:46]

Let's delete the beginDrawing()/endDrawing() methods and inline the skipper and
DrawingRecorder in WebViewImpl::paintPageOverlay. That's the only call site.
Also it's safe to use toWebGraphicsContextImpl() there to cast since the only
call site uses that class. InspectorOverlay does the same thing already.

Please also break some of these changes into new patches.

 #ifndef NDEBUG
     bool m_hasBegunDrawing;
 #endif