Avoid re-rendering stencil clip for every draw with reducable clip stack

src/gpu/GrClipMaskManager.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrClipMaskManager_DEFINED
 #define GrClipMaskManager_DEFINED
 
@@ skipping 85 matching lines @@
      */
     enum ClipMaskType {
         kNone_ClipMaskType,
         kStencil_ClipMaskType,
         kAlpha_ClipMaskType,
     } fCurrClipMaskType;
 
     GrClipMaskCache fAACache;       // cache for the AA path
 
     // Draws the clip into the stencil buffer
-    bool createStencilClipMask(GrReducedClip::InitialState initialState,
+    bool createStencilClipMask(int32_t elementsGenID,
+                               GrReducedClip::InitialState initialState,
                                const GrReducedClip::ElementList& elements,
                                const SkIRect& clipSpaceIBounds,
                                const SkIPoint& clipSpaceToStencilOffset);
     // Creates an alpha mask of the clip. The mask is a rasterization of elements through the
     // rect specified by clipSpaceIBounds.
-    GrTexture* createAlphaClipMask(int32_t clipStackGenID,
+    GrTexture* createAlphaClipMask(int32_t elementsGenID,
                                    GrReducedClip::InitialState initialState,
                                    const GrReducedClip::ElementList& elements,
                                    const SkIRect& clipSpaceIBounds);
     // Similar to createAlphaClipMask but it rasterizes in SW and uploads to the result texture.
-    GrTexture* createSoftwareClipMask(int32_t clipStackGenID,
+    GrTexture* createSoftwareClipMask(int32_t elementsGenID,
                                       GrReducedClip::InitialState initialState,
                                       const GrReducedClip::ElementList& elements,
                                       const SkIRect& clipSpaceIBounds);
 
     // Gets a texture to use for the clip mask. If true is returned then a cached mask was found
     // that already contains the rasterization of the clip stack, otherwise an uninitialized texture
     // is returned. 'willUpload' is set when the alpha mask needs to be uploaded from the CPU.
-    bool getMaskTexture(int32_t clipStackGenID,
+    bool getMaskTexture(int32_t elementsGenID,
                         const SkIRect& clipSpaceIBounds,
                         GrTexture** result,
                         bool willUpload);
 
     bool useSWOnlyPath(const GrReducedClip::ElementList& elements);
 
     // Draws a clip element into the target alpha mask. The caller should have already setup the
     // desired blend operation. Optionally if the caller already selected a path renderer it can
     // be passed. Otherwise the function will select one if the element is a path.
     bool drawElement(GrTexture* target, const SkClipStack::Element*, GrPathRenderer* = NULL);
@@ skipping 26 matching lines @@
      * clipping.
      */
     void adjustStencilParams(GrStencilSettings* settings,
                              StencilClipMode mode,
                              int stencilBitCnt);
 
     typedef SkNoncopyable INHERITED;
 };
 
 #endif // GrClipMaskManager_DEFINED