Add subsets to SkImageGenerator and SkImageCacherator .

src/core/SkImageGenerator.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageGenerator.h"
 #include "SkNextID.h"
 
@@ skipping 86 matching lines @@
     // In order to maintain compatibility with clients that implemented the original
     // onGetYUV8Planes interface, we assume that the color space is JPEG.
     // TODO(rileya): remove this and the old onGetYUV8Planes once clients switch over to
     // the new interface.
     if (colorSpace) {
         *colorSpace = kJPEG_SkYUVColorSpace;
     }
     return this->onGetYUV8Planes(sizes, planes, rowBytes);
 }
 
-GrTexture* SkImageGenerator::generateTexture(GrContext* ctx, SkImageUsageType usage) {
-    if (!ctx) {
+GrTexture* SkImageGenerator::generateTexture(GrContext* ctx, SkImageUsageType usage,
+                                             const SkIRect* subset) {
+    if (subset && !SkIRect::MakeWH(fInfo.width(), fInfo.height()).contains(*subset)) {
         return nullptr;
     }
-    return this->onGenerateTexture(ctx, usage);
+    return this->onGenerateTexture(ctx, usage, subset);
 }
 
 /////////////////////////////////////////////////////////////////////////////////////////////
 
 SkData* SkImageGenerator::onRefEncodedData() {
     return NULL;
 }
 
 bool SkImageGenerator::onGetPixels(const SkImageInfo& info, void* dst, size_t rb,
                                    SkPMColor* colors, int* colorCount) {
@@ skipping 18 matching lines @@
     if (NULL == data) {
         return NULL;
     }
     if (gFactory) {
         if (SkImageGenerator* generator = gFactory(data)) {
             return generator;
         }
     }
     return SkImageGenerator::NewFromEncodedImpl(data);
 }