Force input coverage to be only a byte in gpu shaders.

src/gpu/gl/builders/GrGLProgramBuilder.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 GrGLProgramBuilder_DEFINED
 #define GrGLProgramBuilder_DEFINED
 
@@ skipping 222 matching lines @@
     GrGLProgramBuilder(GrGpuGL*, const GrOptDrawState&);
 
     const GrOptDrawState& optState() const { return fOptState; }
     const GrProgramDesc& desc() const { return fDesc; }
     const GrProgramDesc::KeyHeader& header() const { return fDesc.header(); }
 
     // Generates a name for a variable. The generated string will be name prefixed by the prefix
     // char (unless the prefix is '\0'). It also mangles the name to be stage-specific if we're
     // generating stage code.
     void nameVariable(SkString* out, char prefix, const char* name);
-    void setupUniformColorAndCoverageIfNeeded(GrGLSLExpr4* inputColor, GrGLSLExpr4* inputCoverage);
+    void setupUniformColorAndCoverageIfNeeded(GrGLSLExpr4* inputColor, GrGLSLExpr1* inputCoverage);
     void emitAndInstallProcs(const GrOptDrawState& optState,
                              GrGLSLExpr4* inputColor,
                              GrGLSLExpr4* inputCoverage);
     void emitAndInstallFragProcs(int procOffset, int numProcs, GrGLSLExpr4* inOut);
     template <class Proc>
     void emitAndInstallProc(const Proc&,
                             int index,
                             const ProcKeyProvider&,
                             const GrGLSLExpr4& input,
                             GrGLSLExpr4* output);
@@ skipping 131 matching lines @@
     SkSTArray<2, Transform, true>        fTransforms;
     bool                                 fLocalCoordAttrib;
 };
 
 struct GrGLInstalledFragProcs : public SkRefCnt {
     virtual ~GrGLInstalledFragProcs();
     SkSTArray<8, GrGLInstalledFragProc*, true> fProcs;
 };
 
 #endif