Enable coverage when drawing to the stencil buffer.

src/gpu/GrDrawState.cpp

Index: src/gpu/GrDrawState.cpp
diff --git a/src/gpu/GrDrawState.cpp b/src/gpu/GrDrawState.cpp
index 0a567573cb8aa758bfc0dad361449c8229eb1be1..6c1fa24ec8d31ead6a94a5a0f3181c67bb5bdf4f 100644
--- a/src/gpu/GrDrawState.cpp
+++ b/src/gpu/GrDrawState.cpp
@@ -327,7 +327,7 @@ GrDrawState::BlendOptFlags GrDrawState::getBlendOpts(bool forceCoverage,
     if ((kZero_GrBlendCoeff == *srcCoeff && dstCoeffIsOne) || covIsZero) {
         if (this->getStencil().doesWrite()) {
             return kDisableBlend_BlendOptFlag |
-                   kEmitTransBlack_BlendOptFlag;
+                   kEmitCoverage_BlendOptFlag;
         } else {
             return kSkipDraw_BlendOptFlag;
         }