Add option to control maximum GrBatch lookback

include/gpu/GrContextOptions.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 GrContextOptions_DEFINED
 #define GrContextOptions_DEFINED
 
 #include "SkTypes.h"
 
 struct GrContextOptions {
     GrContextOptions()
         : fDrawPathToCompressedTexture(false)
         , fSuppressPrints(false)
         , fMaxTextureSizeOverride(SK_MaxS32)
         , fMaxTileSizeOverride(0)
         , fSuppressDualSourceBlending(false)
         , fGeometryBufferMapThreshold(-1)
         , fUseDrawInsteadOfPartialRenderTargetWrite(false)
         , fImmediateMode(false)
         , fClipBatchToBounds(false)
         , fDrawBatchBounds(false)
+        , fMaxBatchLookback(-1)
         , fUseShaderSwizzling(false) {}
 
     // EXPERIMENTAL
     // May be removed in the future, or may become standard depending
     // on the outcomes of a variety of internal tests.
     bool fDrawPathToCompressedTexture;
 
     // Suppress prints for the GrContext.
     bool fSuppressPrints;
 
@@ skipping 21 matching lines @@
 
     /** For debugging purposes turn each GrBatch's bounds into a clip rect. This is used to
         verify that the clip bounds are conservative. */
     bool fClipBatchToBounds;
 
     /** For debugging purposes draw a wireframe device bounds rect for each GrBatch. The wire
         frame rect is draw before the GrBatch in order to visualize batches that draw outside
         of their dev bounds. */
     bool fDrawBatchBounds;
 
+    /** For debugging, override the default maximum look-back window for GrBatch combining. */
+    int fMaxBatchLookback;
+
     /** Force us to do all swizzling manually in the shader and don't rely on extensions to do
         swizzling. */
     bool fUseShaderSwizzling;
 };
 
 #endif