Add Dashing gpu effect for simple dashed lines

src/gpu/effects/GrDashingEffect.h

Index: src/gpu/effects/GrDashingEffect.h
diff --git a/src/gpu/effects/GrDashingEffect.h b/src/gpu/effects/GrDashingEffect.h
new file mode 100644
index 0000000000000000000000000000000000000000..129c78491d64aeb4d21c662014eb0d79738dce29
--- /dev/null
+++ b/src/gpu/effects/GrDashingEffect.h
@@ -0,0 +1,75 @@
+
+/*
+ * 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 "GrCoordTransform.h"
+#include "GrDrawTargetCaps.h"
+#include "GrEffect.h"
+#include "GrTypesPriv.h"
+#include "SkPathEffect.h"
+
+class GrGLDashingEffect;
+class SkPath;
+
+/**
+ * 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.
+ */
+
+class GrDashingEffect : public GrEffect {
+public:
+    typedef SkPathEffect::DashInfo DashInfo;
+
+    /**
+     * The effect calculates the coverage for the case of a horizontal line in device space.
+     * The matrix that is passed in should be able to convert a line in source space to a
+     * horizontal line in device space. Additionally, the coord transform matrix should translate
+     * the the start of line to origin, and the shift it along the positive x-axis by the phase
+     * and half the off interval.
+     */
+    static GrEffectRef* Create(GrEffectEdgeType edgeType, const DashInfo& info,
+                               const SkMatrix& matrix, SkScalar strokeWidth);
+
+    virtual ~GrDashingEffect();
+
+    static const char* Name() { return "DashingEffect"; }
+
+    GrEffectEdgeType getEdgeType() const { return fEdgeType; }
+
+    const SkRect& getRect() const { return fRect; }
+
+    const SkScalar& getIntervalLength() const { return fIntervalLength; }
+
+    typedef GrGLDashingEffect GLEffect;
+
+    virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const SK_OVERRIDE;
+
+    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE;
+
+private:
+    GrDashingEffect(GrEffectEdgeType edgeType, const DashInfo& info, const SkMatrix& matrix,
+                    SkScalar strokeWidth);
+
+    virtual bool onIsEqual(const GrEffect& other) const SK_OVERRIDE;
+
+    GrEffectEdgeType    fEdgeType;
+    GrCoordTransform    fCoordTransform;
+    SkRect              fRect;
+    SkScalar            fIntervalLength;
+
+    GR_DECLARE_EFFECT_TEST;
+
+    typedef GrEffect INHERITED;
+};
+
+
+#endif