Determine whether we can tweakAlphaForCoverage during Pipeline/XP creation.

include/gpu/GrXferProcessor.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 GrXferProcessor_DEFINED
 #define GrXferProcessor_DEFINED
 
@@ skipping 55 matching lines @@
          */
         kIgnoreCoverage_OptFlag           = 0x4,
         /**
          * Clear color stages and override input color to that returned by getOptimizations
          */
         kOverrideColor_OptFlag            = 0x8,
         /**
          * Set CoverageDrawing_StateBit
          */
         kSetCoverageDrawing_OptFlag       = 0x10,
+        /**
+         * Can tweak alpha for coverage. Currently this flag should only be used by a batch
+         */
+        kCanTweakAlphaForCoverage_OptFlag = 0x20,
     };
 
     GR_DECL_BITFIELD_OPS_FRIENDS(OptFlags);
 
     /**
      * Determines which optimizations (as described by the ptFlags above) can be performed by
      * the draw with this xfer processor. If this function is called, the xfer processor may change
      * its state to reflected the given blend optimizations. If the XP needs to see a specific input
      * color to blend correctly, it will set the OverrideColor flag and the output parameter
      * overrideColor will be the required value that should be passed into the XP. 
@@ skipping 202 matching lines @@
     enum {
         kIllegalXPFClassID = 0,
     };
     static int32_t gCurrXPFClassID;
 
     typedef GrProgramElement INHERITED;
 };
 
 #endif