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

src/gpu/gl/GrGLVertexArray.h

Index: src/gpu/gl/GrGLVertexArray.h
diff --git a/src/gpu/gl/GrGLVertexArray.h b/src/gpu/gl/GrGLVertexArray.h
index f4eb3d52ca2960e3fdfeea420f182f64a99d5ea6..96e90bc81f0c7da00cda1e1d53d8c22c35108a55 100644
--- a/src/gpu/gl/GrGLVertexArray.h
+++ b/src/gpu/gl/GrGLVertexArray.h
@@ -32,13 +32,15 @@ static inline const GrGLAttribLayout& GrGLAttribTypeToLayout(GrVertexAttribType
         {2, GR_GL_FLOAT, false},         // kVec2f_GrVertexAttribType
         {3, GR_GL_FLOAT, false},         // kVec3f_GrVertexAttribType
         {4, GR_GL_FLOAT, false},         // kVec4f_GrVertexAttribType
+        {1, GR_GL_UNSIGNED_BYTE, true},  // kUByte_GrVertexAttribType
         {4, GR_GL_UNSIGNED_BYTE, true},  // kVec4ub_GrVertexAttribType
     };
     GR_STATIC_ASSERT(0 == kFloat_GrVertexAttribType);
     GR_STATIC_ASSERT(1 == kVec2f_GrVertexAttribType);
     GR_STATIC_ASSERT(2 == kVec3f_GrVertexAttribType);
     GR_STATIC_ASSERT(3 == kVec4f_GrVertexAttribType);
-    GR_STATIC_ASSERT(4 == kVec4ub_GrVertexAttribType);
+    GR_STATIC_ASSERT(4 == kUByte_GrVertexAttribType);
+    GR_STATIC_ASSERT(5 == kVec4ub_GrVertexAttribType);
     GR_STATIC_ASSERT(SK_ARRAY_COUNT(kLayouts) == kGrVertexAttribTypeCount);
     return kLayouts[type];
 }