GPU implementation of drawRegion()

Nexus 6P drawregion Bench Performance
Before 48.0ms
After  3.57ms

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2267273006

Review-Url: https://codereview.chromium.org/2267273006

2 files changed, 19 insertions, 1 deletions

diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index 780af107af..d9b3282d3e 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -708,6 +708,10 @@ public:
         @param paint    The paint used to draw the region
     */
     void drawRegion(const SkRegion& region, const SkPaint& paint) {
+        if (region.isEmpty()) {
+            return;
+        }
+
         this->onDrawRegion(region, paint);
     }
 
diff --git a/include/gpu/GrDrawContext.h b/include/gpu/GrDrawContext.h
index 993bb56f9e..29c7d1c12e 100644
--- a/include/gpu/GrDrawContext.h
+++ b/include/gpu/GrDrawContext.h
@@ -216,7 +216,21 @@ public:
                    const SkRSXform xform[],
                    const SkRect texRect[],
                    const SkColor colors[]);
-    
+
+    /**
+     * Draws a region.
+     *
+     * @param paint         describes how to color pixels
+     * @param viewMatrix    transformation matrix
+     * @param region        the region to be drawn
+     * @param style         style to apply to the region
+     */
+    void drawRegion(const GrClip&,
+                    const GrPaint& paint,
+                    const SkMatrix& viewMatrix,
+                    const SkRegion& region,
+                    const GrStyle& style);
+
     /**
      * Draws an oval.
      *