Make mixed samples contingent on auxiliary extensions

src/gpu/GrDrawTargetCaps.h

Index: src/gpu/GrDrawTargetCaps.h
diff --git a/src/gpu/GrDrawTargetCaps.h b/src/gpu/GrDrawTargetCaps.h
index c1b7381cc20f43a350ac920c0da42859bc062c50..3381bd36b4e0ba8dc123e5cc9d36123413935518 100644
--- a/src/gpu/GrDrawTargetCaps.h
+++ b/src/gpu/GrDrawTargetCaps.h
@@ -69,6 +69,7 @@ public:
     bool pathRenderingSupport() const { return fPathRenderingSupport; }
     bool dstReadInShaderSupport() const { return fDstReadInShaderSupport; }
     bool dualSourceBlendingSupport() const { return fDualSourceBlendingSupport; }
+    bool mixedSamplesSupport() const { return fMixedSamplesSupport; }
 
     /**
     * Get the precision info for a variable of type kFloat_GrSLType, kVec2f_GrSLType, etc in a
@@ -94,6 +95,7 @@ protected:
     bool fPathRenderingSupport : 1;
     bool fDstReadInShaderSupport : 1;
     bool fDualSourceBlendingSupport : 1;
+    bool fMixedSamplesSupport : 1;
 
     bool fShaderPrecisionVaries;
     PrecisionInfo fFloatPrecisions[kGrShaderTypeCount][kGrSLPrecisionCount];