Verify paintedOutputOfObjectHasNoEffectRegardlessOfSize during painting

third_party/WebKit/Source/platform/graphics/paint/DisplayItemClient.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DisplayItemClient_h
 #define DisplayItemClient_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/graphics/PaintInvalidationReason.h"
@@ skipping 37 matching lines @@
   virtual ~DisplayItemClient() {}
 #endif
 
   virtual String debugName() const = 0;
 
   // The visual rect of this DisplayItemClient, in the object space of the
   // object that owns the GraphicsLayer, i.e. offset by
   // offsetFromLayoutObjectWithSubpixelAccumulation().
   virtual LayoutRect visualRect() const = 0;
 
+  // This is declared here instead of in LayoutObject for verifying the
+  // condition in DrawingRecorder.
+  // Returns true if the object itself will not generate any effective painted
+  // output no matter what size the object is. For example, this function can
+  // return false for an object whose size is currently 0x0 but would have
+  // effective painted output if it was set a non-empty size. It's used to skip
+  // unforced paint invalidation of LayoutObjects (which is when
+  // shouldDoFullPaintInvalidation is false, but mayNeedPaintInvalidation or
+  // childShouldCheckForPaintInvalidation is true) to avoid unnecessary paint
+  // invalidations of empty areas covered by such objects.
+  virtual bool paintedOutputOfObjectHasNoEffectRegardlessOfSize() const {

[chrishtr, 2016/12/05 21:21:12]

Remove this method from LayoutObject?

[Xianzhu, 2016/12/05 21:29:15]

Done.

+    return false;
+  }
+
   void setDisplayItemsUncached(
       PaintInvalidationReason reason = PaintInvalidationFull) const {
     m_cacheGenerationOrInvalidationReason.invalidate(reason);
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
     // Clear should-keep-alive of DisplayItemClients in a subsequence if this
     // object is a subsequence.
     endShouldKeepAliveAllClients(this);
 #endif
   }
 
@@ skipping 96 matching lines @@
   return &client1 == &client2;
 }
 inline bool operator!=(const DisplayItemClient& client1,
                        const DisplayItemClient& client2) {
   return &client1 != &client2;
 }
 
 }  // namespace blink
 
 #endif  // DisplayItemClient_h