Revert of Remove gpu support for willUseHWAALines.

src/gpu/GrDrawState.cpp

Index: src/gpu/GrDrawState.cpp
diff --git a/src/gpu/GrDrawState.cpp b/src/gpu/GrDrawState.cpp
index 1b40642251e87219f321d6a3e6aeeb836db6e84c..02c7920f5d07c778870ae7ef972b733316c61c73 100644
--- a/src/gpu/GrDrawState.cpp
+++ b/src/gpu/GrDrawState.cpp
@@ -339,7 +339,8 @@
     // (0,1). The same applies when coverage is known to be 0.
     if ((kZero_GrBlendCoeff == *srcCoeff && dstCoeffIsOne) || covIsZero) {
         if (this->getStencil().doesWrite()) {
-            return kEmitCoverage_BlendOptFlag;
+            return kDisableBlend_BlendOptFlag |
+                   kEmitCoverage_BlendOptFlag;
         } else {
             return kSkipDraw_BlendOptFlag;
         }
@@ -358,14 +359,13 @@
             if (kOne_GrBlendCoeff == *srcCoeff) {
                 // if there is no coverage and coeffs are (1,0) then we
                 // won't need to read the dst at all, it gets replaced by src
-                *dstCoeff = kZero_GrBlendCoeff;
-                return kNone_BlendOpt;
+                return kDisableBlend_BlendOptFlag;
             } else if (kZero_GrBlendCoeff == *srcCoeff) {
                 // if the op is "clear" then we don't need to emit a color
                 // or blend, just write transparent black into the dst.
                 *srcCoeff = kOne_GrBlendCoeff;
                 *dstCoeff = kZero_GrBlendCoeff;
-                return kEmitTransBlack_BlendOptFlag;
+                return kDisableBlend_BlendOptFlag | kEmitTransBlack_BlendOptFlag;
             }
         }
     } else if (this->isCoverageDrawing()) {
@@ -399,7 +399,13 @@
             return  kCoverageAsAlpha_BlendOptFlag;
         }
     }
-
+    if (kOne_GrBlendCoeff == *srcCoeff &&
+        kZero_GrBlendCoeff == *dstCoeff &&
+        this->willEffectReadDstColor()) {
+        // In this case the shader will fully resolve the color, coverage, and dst and we don't
+        // need blending.
+        return kDisableBlend_BlendOptFlag;
+    }
     return kNone_BlendOpt;
 }