Add Dashing gpu effect for simple dashed lines

BUG=skia:
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/274673004

git-svn-id: http://skia.googlecode.com/svn/trunk@14775 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/SkGpuDevice.h b/include/gpu/SkGpuDevice.h
index 15951aa..d2df32c 100644
--- a/include/gpu/SkGpuDevice.h
+++ b/include/gpu/SkGpuDevice.h
@@ -219,6 +219,8 @@
                          int tileSize,
                          bool bicubic);
 
+    bool drawDashLine(const SkPoint pts[2], const SkPaint& paint);
+
     static SkPicture::AccelData::Key ComputeAccelDataKey();
 
     typedef SkBitmapDevice INHERITED;