Cache the GrEffect used for text rendering in GrBitmapTextContext.

include/gpu/GrCacheable.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrCacheable_DEFINED
 #define GrCacheable_DEFINED
 
@@ skipping 23 matching lines @@
      * should no longer count against the GrResourceCache budget.
      *
      * @return true if this resource is still holding GPU memory
      *         false otherwise.
      */
     virtual bool isValidOnGpu() const = 0;
 
     void setCacheEntry(GrResourceCacheEntry* cacheEntry) { fCacheEntry = cacheEntry; }
     GrResourceCacheEntry* getCacheEntry() { return fCacheEntry; }
 
+    /**
+     * Gets an id that is unique for this GrCacheable object. It is static in that it does
+     * not change when the content of the GrCacheable object changes. This will never return
+     * 0.
+     */
+    uint32_t getGenerationID() const;
+
 protected:
-    GrCacheable() : fCacheEntry(NULL) {}
+    GrCacheable()
+        : fCacheEntry(NULL)
+        , fGenID(0) {}
 
     bool isInCache() const { return NULL != fCacheEntry; }
 
     /**
      * This entry point should be called whenever gpuMemorySize() begins
      * reporting a different size. If the object is in the cache, it will call
      * gpuMemorySize() immediately and pass the new size on to the resource
      * cache.
      */
     void didChangeGpuMemorySize() const;
 
 private:
-    GrResourceCacheEntry* fCacheEntry;  // NULL if not in cache
+    GrResourceCacheEntry*   fCacheEntry;  // NULL if not in cache
+    mutable uint32_t        fGenID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif