SkPDF: properly dedup bitmaps in shaders

src/pdf/SkBitmapKey.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkBitmapKey_DEFINED
 #define SkBitmapKey_DEFINED
 
 #include "SkBitmap.h"
 #include "SkImage.h"
 #include "SkCanvas.h"
 
 class SkBitmapKey {
 public:
     SkBitmapKey() : fSubset(SkIRect::MakeEmpty()), fID(0) {}
     explicit SkBitmapKey(const SkBitmap& bm)
         : fSubset(bm.getSubset()), fID(bm.getGenerationID()) {}
     explicit SkBitmapKey(const SkImage* img)
         : fSubset(img ? img->bounds() : SkIRect::MakeEmpty())
         , fID(img ? img->uniqueID() : 0) {}
     explicit SkBitmapKey(const sk_sp<SkImage> img)
         : fSubset(img->bounds()), fID(img->uniqueID()) {}
     bool operator==(const SkBitmapKey& rhs) const {
         return fID == rhs.fID && fSubset == rhs.fSubset;
     }
     bool operator!=(const SkBitmapKey& rhs) const { return !(*this == rhs); }
+    uint32_t id() const { return fID; }
 
 private:
     SkIRect fSubset;
     uint32_t fID;
 };
 
 /**
    This wraps a thing that could either be a bitmap or a image and
    abstracts out some common tasks.
  */
@@ skipping 19 matching lines @@
         }
     }
 
 private:
     SkBitmap fBitmap;
     SkImage* fImage; // non-owning; when drawImage starts passing a sk_sp<>,
                      // we can take a const ref to that sk_sp<>.
 };
 
 #endif  // SkBitmapKey_DEFINED