Check that coverage FPs are compatible with alpha as coverage

Change-Id: Ic3b6a02248d571e82f6729827c199d358fb75114
Reviewed-on: https://skia-review.googlesource.com/8508
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index ead4ed6..6b7d0ba 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -466,7 +466,8 @@
             optFlags |= GrXferProcessor::kIgnoreColor_OptFlag;
         }
         if (analysis.fColorPOI.allProcessorsCompatibleWithCoverageAsAlpha() &&
-            fBlendFormula.canTweakAlphaForCoverage() && !analysis.fCoveragePOI.isLCDCoverage()) {
+            analysis.fCoveragePOI.allProcessorsCompatibleWithCoverageAsAlpha() &&
+            fBlendFormula.canTweakAlphaForCoverage()) {
             optFlags |= GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag;
         }
     }