Compute style-determined compositing reasons during recalc style

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index c47be6490ca11ad4b7035a408ddf811fd9988690..bf0ca8532c64ade336c2d1b92f4ed091aa250edd 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -1185,11 +1185,12 @@ RenderLayer* RenderLayer::enclosingFilterLayer(IncludeSelfOrNot includeSelf) con
     return 0;
 }
 
-void RenderLayer::setCompositingReasons(CompositingReasons reasons)
+void RenderLayer::setCompositingReasons(CompositingReasons reasons, CompositingReasons mask)
 {
-    if (m_compositingProperties.compositingReasons == reasons)
+    ASSERT(reasons == (reasons & mask));
+    if ((m_compositingProperties.compositingReasons & mask) == (reasons & mask))
         return;
-    m_compositingProperties.compositingReasons = reasons;
+    m_compositingProperties.compositingReasons = (reasons & mask) | (m_compositingProperties.compositingReasons & ~mask);
     m_clipper.setCompositingClipRectsDirty();
 }
 
@@ -3908,6 +3909,8 @@ void RenderLayer::styleChanged(StyleDifference diff, const RenderStyle* oldStyle
         updateFilters(oldStyle, renderer()->style());
     }
 
+    compositor()->updateStyleDeterminedCompositingReasons(this);
+
     // FIXME: Remove incremental compositing updates after fixing the chicken/egg issues
     // https://code.google.com/p/chromium/issues/detail?id=343756
     DisableCompositingQueryAsserts disabler;