Don't turn on dither for saveLayers which have no paint

src/core/SkCanvas.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkCanvasPriv.h"
 #include "SkBitmapDevice.h"
@@ skipping 1186 matching lines @@
         iter.fDevice->drawBitmap(iter, bitmap, matrix, looper.paint());
     }
 
     LOOPER_END
 }
 
 void SkCanvas::internalDrawDevice(SkBaseDevice* srcDev, int x, int y,
                                   const SkPaint* paint) {
     SkPaint tmp;
     if (NULL == paint) {
-        tmp.setDither(true);
         paint = &tmp;
     }
 
     LOOPER_BEGIN_DRAWDEVICE(*paint, SkDrawFilter::kBitmap_Type)
     while (iter.next()) {
         SkBaseDevice* dstDev = iter.fDevice;
         paint = &looper.paint();
         SkImageFilter* filter = paint->getImageFilter();
         SkIPoint pos = { x - iter.getX(), y - iter.getY() };
         if (filter && !dstDev->canHandleImageFilter(filter)) {
@@ skipping 1335 matching lines @@
     }
 
     if (matrix) {
         canvas->concat(*matrix);
     }
 }
 
 SkAutoCanvasMatrixPaint::~SkAutoCanvasMatrixPaint() {
     fCanvas->restoreToCount(fSaveCount);
 }