Fix clipping when all analytic FP creations can be skipped

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
 
 #include "GrPipelineBuilder.h"
@@ skipping 69 matching lines @@
         // Draw to the clip bit of the stencil buffer
         kModifyClip_StencilClipMode,
         // Clip against the existing representation of the clip in the high bit
         // of the stencil buffer.
         kRespectClip_StencilClipMode,
         // Neither writing to nor clipping against the clip bit.
         kIgnoreClip_StencilClipMode,
     };
 
     // Attempts to install a series of coverage effects to implement the clip. Return indicates
-    // whether the element list was successfully converted to effects.
-    const GrFragmentProcessor* getAnalyticClipProcessor(const GrReducedClip::ElementList&,
-                                                        const SkVector& clipOffset,
-                                                        const SkRect* devBounds);
+    // whether the element list was successfully converted to processors. *fp may be nullptr even
+    // when the function succeeds because all the elements were ignored. TODO: Make clip reduction
+    // bounds-aware and stop checking bounds in this function.
+    bool getAnalyticClipProcessor(const GrReducedClip::ElementList&,
+                                  SkVector& clipOffset,
+                                  const SkRect* devBounds,
+                                  const GrFragmentProcessor** fp);
 
     // Draws the clip into the stencil buffer
     bool createStencilClipMask(GrRenderTarget*,
                                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
@@ skipping 59 matching lines @@
     GrTexture* createCachedMask(int width, int height, const GrUniqueKey& key, bool renderTarget);
 
     static const int kMaxAnalyticElements = 4;
 
     GrDrawTarget*   fDrawTarget;    // This is our owning draw target.
     StencilClipMode fClipMode;
 
     typedef SkNoncopyable INHERITED;
 };
 #endif // GrClipMaskManager_DEFINED