Add subsets to SkImageGenerator and SkImageCacherator .

src/core/SkImageCacherator.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageCacherator_DEFINED
 #define SkImageCacherator_DEFINED
 
 #include "SkImageGenerator.h"
 
 class GrContext;
 class SkBitmap;
 
 /*
  *  Internal class to manage caching the output of an ImageGenerator.
  */
 class SkImageCacherator {
 public:
     // Takes ownership of the generator
-    static SkImageCacherator* NewFromGenerator(SkImageGenerator*);
+    static SkImageCacherator* NewFromGenerator(SkImageGenerator*, const SkIRect* subset = nullptr);
 
     ~SkImageCacherator();
 
-    const SkImageInfo& info() const { return fGenerator->getInfo(); }
-    SkImageGenerator* generator() const { return fGenerator; }
+    const SkImageInfo& info() const { return fInfo; }
+    uint32_t uniqueID() const { return fUniqueID; }
 
     /**
      *  On success (true), bitmap will point to the pixels for this generator. If this returns
      *  false, the bitmap will be reset to empty.
      */
     bool lockAsBitmap(SkBitmap*);
 
     /**
      *  Returns a ref() on the texture produced by this generator. The caller must call unref()
      *  when it is done. Will return NULL on failure.
      *
      *  The caller is responsible for calling texture->unref() when they are done.
      */
     GrTexture* lockAsTexture(GrContext*, SkImageUsageType);
 
 private:
-    SkImageCacherator(SkImageGenerator* gen);
+    SkImageCacherator(SkImageGenerator*, const SkImageInfo&, const SkIPoint&, uint32_t uniqueID);
 
     bool tryLockAsBitmap(SkBitmap*);
     GrTexture* tryLockAsTexture(GrContext*, SkImageUsageType);
 
-    SkImageGenerator* fGenerator;
+    SkImageGenerator*   fGenerator;
+    const SkImageInfo   fInfo;
+    const SkIPoint      fOrigin;
+    const uint32_t      fUniqueID;
 };
 
 #endif