Reduce texture uploads during scrollbar invalidations.

cc/LayerTextureUpdater.h

Index: cc/LayerTextureUpdater.h
diff --git a/cc/LayerTextureUpdater.h b/cc/LayerTextureUpdater.h
index 0426bc42655d5f1bf7e7e1e8239ffb2a80c86f86..b6dc763168935447b708b6a352675b368a9f3d5b 100644
--- a/cc/LayerTextureUpdater.h
+++ b/cc/LayerTextureUpdater.h
@@ -60,6 +60,9 @@ public:
     // then this region should be ignored in preference for the entire layer's area.
     virtual void prepareToUpdate(const IntRect& contentRect, const IntSize& tileSize, float contentsWidthScale, float contentsHeightScale, IntRect& resultingOpaqueRect, CCRenderingStats&) { }
 
+    // Use after prepareToUpdate, allows checking if the texture contents will change, to avoid unecessary uploads.
+    virtual bool pixelsDidChange() const;

[jamesr, 2012/10/03 19:28:02]

this is unnecessary.  Keep the more specific type in ScrollbarLayerChromium

[enne (OOO), 2012/10/03 19:31:43]

Please don't do this.

updatePart is a non-virtual member function on ScrollbarLayerChromium.  There
are no derived classes from ScrollbarLayerChromium.  There's no impact other
than to ScrollbarLayerChromium to change the member variable types and the
updatePart signature to the derived updater type.  I think that's a lot cleaner
than exposing this to all updaters.

[wjmaclean, 2012/10/03 20:14:30]

Done.

NP, I just wasn't sure if you'd want me to change the member var type on SLC.

[wjmaclean, 2012/10/03 20:14:30]

Done.

+
     // Set true by the layer when it is known that the entire output is going to be opaque.
     virtual void setOpaque(bool) { }
 };