Implement will-change-based GPU rasterization hint

Source/core/rendering/style/RenderStyle.cpp

Index: Source/core/rendering/style/RenderStyle.cpp
diff --git a/Source/core/rendering/style/RenderStyle.cpp b/Source/core/rendering/style/RenderStyle.cpp
index 75558d6645ce33b6fce395b5cdfca14d44e878f5..e421e2e41e6e13f88b9113a23e53dd1046f1ea8b 100644
--- a/Source/core/rendering/style/RenderStyle.cpp
+++ b/Source/core/rendering/style/RenderStyle.cpp
@@ -651,7 +651,8 @@ StyleDifference RenderStyle::repaintOnlyDiff(const RenderStyle* other, unsigned&
             || rareNonInheritedData->m_perspective != other->rareNonInheritedData->m_perspective
             || rareNonInheritedData->m_perspectiveOriginX != other->rareNonInheritedData->m_perspectiveOriginX
             || rareNonInheritedData->m_perspectiveOriginY != other->rareNonInheritedData->m_perspectiveOriginY
-            || hasWillChangeCompositingHint() != other->hasWillChangeCompositingHint())
+            || hasWillChangeCompositingHint() != other->hasWillChangeCompositingHint()
+            || hasWillChangeGpuRasterizationHint() != other->hasWillChangeGpuRasterizationHint())
             return StyleDifferenceRecompositeLayer;
     }
 
@@ -851,6 +852,23 @@ bool RenderStyle::hasWillChangeCompositingHint() const
     return false;
 }
 
+bool RenderStyle::hasWillChangeGpuRasterizationHint() const
+{
+    if (willChangeContents())
+        return true;
+
+    for (size_t i = 0; i < rareNonInheritedData->m_willChange->m_properties.size(); ++i) {
+        switch (rareNonInheritedData->m_willChange->m_properties[i]) {
+        case CSSPropertyWidth:
+        case CSSPropertyHeight:

[Ian Vollick, 2014/03/07 15:33:52]

Dumb question: do we want background position/color to be in the list here, too?

[ajuma, 2014/03/07 17:03:41]

Good idea, I've added these to the list.

+            return true;
+        default:
+            break;
+        }
+    }
+    return false;
+}
+
 inline bool requireTransformOrigin(const Vector<RefPtr<TransformOperation> >& transformOperations, RenderStyle::ApplyTransformOrigin applyOrigin)
 {
     // transform-origin brackets the transform with translate operations.