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

src/gpu/gl/builders/GrGLProgramBuilder.h

Index: src/gpu/gl/builders/GrGLProgramBuilder.h
diff --git a/src/gpu/gl/builders/GrGLProgramBuilder.h b/src/gpu/gl/builders/GrGLProgramBuilder.h
index 0abdf0a12229fc9928510782e485311bd8c2b5f3..4bcf50be6a10913637eb0118c5b1d3a7232b56f4 100644
--- a/src/gpu/gl/builders/GrGLProgramBuilder.h
+++ b/src/gpu/gl/builders/GrGLProgramBuilder.h
@@ -240,7 +240,7 @@ protected:
     // 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);