initial preroll api

src/image/SkImage.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkImageGenerator.h"
@@ skipping 100 matching lines @@
         }
     }
 
     if (NULL == subset && this->width() == newWidth && this->height() == newHeight) {
         return SkRef(const_cast<SkImage*>(this));
     }
 
     return as_IB(this)->onNewImage(newWidth, newHeight, subset, quality);
 }
 
+void SkImage::preroll() const {
+    as_IB(this)->onPreroll();
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 static bool raster_canvas_supports(const SkImageInfo& info) {
     switch (info.colorType()) {
         case kN32_SkColorType:
             return kUnpremul_SkAlphaType != info.alphaType();
         case kRGB_565_SkColorType:
             return true;
         case kAlpha_8_SkColorType:
             return true;
@@ skipping 41 matching lines @@
     surface->getCanvas()->translate(-src.x(), -src.y());
 
     SkPaint paint;
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     paint.setFilterQuality(quality);
     surface->getCanvas()->drawImage(this, 0, 0, &paint);
     return surface->newImageSnapshot();
 }