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

src/gpu/GrAAHairLinePathRenderer.cpp

Index: src/gpu/GrAAHairLinePathRenderer.cpp
diff --git a/src/gpu/GrAAHairLinePathRenderer.cpp b/src/gpu/GrAAHairLinePathRenderer.cpp
index 6990b7e9fb5913242803a34a6f0aadf848e1b108..0ffbc9dbcd90d38e963ae9d17c5da6615d714f38 100644
--- a/src/gpu/GrAAHairLinePathRenderer.cpp
+++ b/src/gpu/GrAAHairLinePathRenderer.cpp
@@ -650,7 +650,7 @@ extern const GrVertexAttrib gHairlineBezierAttribs[] = {
 // position + coverage
 extern const GrVertexAttrib gHairlineLineAttribs[] = {
     {kVec2f_GrVertexAttribType,  0,               kPosition_GrVertexAttribBinding},
-    {kVec4ub_GrVertexAttribType, sizeof(SkPoint), kCoverage_GrVertexAttribBinding},
+    {kUByte_GrVertexAttribType, sizeof(SkPoint), kCoverage_GrVertexAttribBinding},
 };
 
 };