Implement a persistent uniqueID-based cache for SkImageFilter.

include/core/SkReadBuffer.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkReadBuffer_DEFINED
 #define SkReadBuffer_DEFINED
 
@@ skipping 28 matching lines @@
     virtual ~SkReadBuffer();
 
     enum Version {
         kFilterLevelIsEnum_Version         = 23,
         kGradientFlippedFlag_Version       = 24,
         kDashWritesPhaseIntervals_Version  = 25,
         kColorShaderNoBool_Version         = 26,
         kNoUnitMappers_Version             = 27,
         kNoMoreBitmapFlatten_Version       = 28,
         kSimplifyLocalMatrix_Version       = 30,
+        kImageFilterUniqueID_Version       = 31,
     };
 
     /**
      *  Returns true IFF the version is older than the specified version.
      */
     bool isVersionLT(Version targetVersion) const {
         SkASSERT(targetVersion > 0);
         return fVersion > 0 && fVersion < targetVersion;
     }
 
@@ skipping 164 matching lines @@
     SkPicture::InstallPixelRefProc fBitmapDecoder;
 
 #ifdef DEBUG_NON_DETERMINISTIC_ASSERT
     // Debugging counter to keep track of how many bitmaps we
     // have decoded.
     int fDecodedBitmapIndex;
 #endif // DEBUG_NON_DETERMINISTIC_ASSERT
 };
 
 #endif // SkReadBuffer_DEFINED