change SkDraw and all Blitters to use pixmap instead of bitmap

src/effects/SkLayerRasterizer.cpp

Index: src/effects/SkLayerRasterizer.cpp
diff --git a/src/effects/SkLayerRasterizer.cpp b/src/effects/SkLayerRasterizer.cpp
index d3e112c3a4b836118be46258c5f3d1b9fb181ab3..8403d06147a602969aeb8c5f5d1af00a3fe062f5 100644
--- a/src/effects/SkLayerRasterizer.cpp
+++ b/src/effects/SkLayerRasterizer.cpp
@@ -116,9 +116,12 @@ bool SkLayerRasterizer::onRasterize(const SkPath& path, const SkMatrix& matrix,
     }
 
     if (SkMask::kJustComputeBounds_CreateMode != mode) {
-        SkBitmap        device;
-        SkRasterClip    rectClip;
         SkDraw          draw;
+        if (!draw.fDst.reset(*mask)) {
+            return false;
+        }
+
+        SkRasterClip    rectClip;
         SkMatrix        translatedMatrix;  // this translates us to our local pixels
         SkMatrix        drawMatrix;        // this translates the path by each layer's offset
 
@@ -128,9 +131,6 @@ bool SkLayerRasterizer::onRasterize(const SkPath& path, const SkMatrix& matrix,
         translatedMatrix.postTranslate(-SkIntToScalar(mask->fBounds.fLeft),
                                        -SkIntToScalar(mask->fBounds.fTop));
 
-        device.installMaskPixels(*mask);
-
-        draw.fBitmap    = &device;
         draw.fMatrix    = &drawMatrix;
         draw.fRC        = &rectClip;
         draw.fClip      = &rectClip.bwRgn();