Make GrDashEffect take a AA mode enum.

src/gpu/effects/GrDashingEffect.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrDashingEffect_DEFINED
 #define GrDashingEffect_DEFINED
 
 #include "GrColor.h"
 #include "GrTypesPriv.h"
 #include "SkPathEffect.h"
 
 class GrClip;
 class GrDrawBatch;
 class GrStyle;
 
 namespace GrDashingEffect {
+    enum class AAMode {
+        kNone,
+        kCoverage,
+        kCoverageWithMSAA,
+    };
+    static const int kAAModeCnt = static_cast<int>(AAMode::kCoverageWithMSAA) + 1;
+
     GrDrawBatch* CreateDashLineBatch(GrColor,
                                      const SkMatrix& viewMatrix,
                                      const SkPoint pts[2],
-                                     bool useAA,
-                                     bool msaaIsEnabled,
+                                     AAMode,
                                      const GrStyle& style);
     bool CanDrawDashLine(const SkPoint pts[2], const GrStyle& style,
                          const SkMatrix& viewMatrix);
 }
 
 #endif