Backed out changeset f251bbc37cb0 (bug 1258168) for failing Reftest(R) 817019-1.html on Windows 8 x64. r=backout on a CLOSED TREE

gfx/2d/DrawTargetD2D1.cpp

@@ -1786,7 +1786,7 @@ DrawTargetD2D1::PushD2DLayer(ID2D1DeviceContext *aDC, ID2D1Geometry *aGeometry,
 {
   D2D1_LAYER_OPTIONS1 options = D2D1_LAYER_OPTIONS1_NONE;
 
-  if (CurrentLayer().mIsOpaque || aForceIgnoreAlpha) {
+  if (aDC->GetPixelFormat().alphaMode == D2D1_ALPHA_MODE_IGNORE || aForceIgnoreAlpha) {
     options = D2D1_LAYER_OPTIONS1_IGNORE_ALPHA | D2D1_LAYER_OPTIONS1_INITIALIZE_FROM_BACKGROUND;
   }