Add Dashing gpu effect for simple dashed lines

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 "GrTypesPriv.h"
+#include "SkPathEffect.h"
+
+class SkGpuDevice;
+
+class GrGLDashingEffect;
+class SkPath;
+
+namespace GrDashingEffect {
+    bool DrawDashLine(const SkPoint pnts[2], const SkPaint& paint, SkGpuDevice* dev);
+
+    /**
+     * An effect that renders a dashed line. It is intended to be used as a coverage effect.
+     * The effect is meant for dashed lines that only have a single on/off interval pair.
+     * Bounding geometry is rendered and the effect computes coverage based on the fragment's
+     * position relative to the dashed line.
+     */
+    GrEffectRef* Create(GrEffectEdgeType edgeType, const SkPathEffect::DashInfo& info,
+                        const SkMatrix& matrix, SkScalar strokeWidth);
+}
+
+#endif