Bug 1011062. Add a fast path to DrawTargetSkia::MaskSurface(). r=gw280

This should speed things up significantly by avoid a bunch
of unneeded work.

--HG--
extra : rebase_source : 1194a825a5a9e5e86a94ba6c6c67f959051f1da3

gfx/2d/DrawTargetSkia.cpp

@@ -552,21 +552,26 @@ DrawTargetSkia::MaskSurface(const Pattern &aSource,
   MarkChanged();
   AutoPaintSetup paint(mCanvas.get(), aOptions, aSource);
 
-  SkPaint maskPaint;
-  TempBitmap tmpBitmap;
-  SetPaintPattern(maskPaint, SurfacePattern(aMask, ExtendMode::CLAMP), tmpBitmap);
+  TempBitmap bitmap = GetBitmapForSurface(aMask);
+  if (bitmap.mBitmap.colorType() == kAlpha_8_SkColorType) {
+    mCanvas->drawBitmap(bitmap.mBitmap, aOffset.x, aOffset.y, &paint.mPaint);
+  } else {
+    SkPaint maskPaint;
+    TempBitmap tmpBitmap;
+    SetPaintPattern(maskPaint, SurfacePattern(aMask, ExtendMode::CLAMP), tmpBitmap);
 
-  SkMatrix transform = maskPaint.getShader()->getLocalMatrix();
-  transform.postTranslate(SkFloatToScalar(aOffset.x), SkFloatToScalar(aOffset.y));
-  maskPaint.getShader()->setLocalMatrix(transform);
+    SkMatrix transform = maskPaint.getShader()->getLocalMatrix();
+    transform.postTranslate(SkFloatToScalar(aOffset.x), SkFloatToScalar(aOffset.y));
+    maskPaint.getShader()->setLocalMatrix(transform);
 
-  SkLayerRasterizer *raster = new SkLayerRasterizer();
-  raster->addLayer(maskPaint);
-  SkSafeUnref(paint.mPaint.setRasterizer(raster));
+    SkLayerRasterizer *raster = new SkLayerRasterizer();
+    raster->addLayer(maskPaint);
+    SkSafeUnref(paint.mPaint.setRasterizer(raster));
 
-  IntSize size = aMask->GetSize();
-  Rect rect = Rect(aOffset.x, aOffset.y, size.width, size.height);
-  mCanvas->drawRect(RectToSkRect(rect), paint.mPaint);
+    IntSize size = aMask->GetSize();
+    Rect rect = Rect(aOffset.x, aOffset.y, size.width, size.height);
+    mCanvas->drawRect(RectToSkRect(rect), paint.mPaint);
+  }
 }
 
 TemporaryRef<SourceSurface>