Determine whether we can tweakAlphaForCoverage during Pipeline/XP creation.

include/gpu/GrInvariantOutput.h

Index: include/gpu/GrInvariantOutput.h
diff --git a/include/gpu/GrInvariantOutput.h b/include/gpu/GrInvariantOutput.h
index 269748a026c8f35b5b80cc02895b513f6c98d9de..4977333de4e80779432c0eb20289ad5065f47ae3 100644
--- a/include/gpu/GrInvariantOutput.h
+++ b/include/gpu/GrInvariantOutput.h
@@ -210,6 +210,7 @@ private:
     bool willUseInputColor() const { return fWillUseInputColor; }
     void resetWillUseInputColor() { fWillUseInputColor = true; }
 
+    bool allStagesMulInput() const { return !fNonMulStageFound; }
     void resetNonMulStageFound() { fNonMulStageFound = false; }
 
     bool isLCDCoverage() const { return fIsLCDCoverage; }