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

src/gpu/GrDrawState.cpp

Index: src/gpu/GrDrawState.cpp
diff --git a/src/gpu/GrDrawState.cpp b/src/gpu/GrDrawState.cpp
index e1fa6da8774307cf1c115db2ba64d6e772e857a6..a6334dcf962b2958e8223bb413d679bb7db60b58 100644
--- a/src/gpu/GrDrawState.cpp
+++ b/src/gpu/GrDrawState.cpp
@@ -389,7 +389,7 @@ bool GrDrawState::hasSolidCoverage() const {
     }
 
     GrProcessor::InvariantOutput inout;
-    inout.fIsSingleComponent = false;
+    inout.fIsSingleComponent = true;

[bsalomon, 2014/10/24 15:13:59]

I think it is time to enforce that the coverage attr is single component now
that we're init'ing this to true when it is present.

     // Initialize to an unknown starting coverage if per-vertex coverage is specified.
     if (this->hasCoverageVertexAttribute()) {
         inout.fValidFlags = 0;
@@ -738,7 +738,7 @@ bool GrDrawState::srcAlphaWillBeOne() const {
         // The shader generated for coverage drawing runs the full coverage computation and then
         // makes the shader output be the multiplication of color and coverage. We mirror that here.
         GrProcessor::InvariantOutput inoutCoverage;
-        inoutCoverage.fIsSingleComponent = false;
+        inoutCoverage.fIsSingleComponent = true;
         if (this->hasCoverageVertexAttribute()) {
             inoutCoverage.fValidFlags = 0;
             inoutCoverage.fColor = 0; // suppresses any warnings.