Set scissor to clip bounding box when using GrConvexPolyEffect

BUG=skia:2051
R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/156843005

git-svn-id: http://skia.googlecode.com/svn/trunk@13361 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrClipMaskManager.cpp b/src/gpu/GrClipMaskManager.cpp
index 340ede0..c1c5973 100644
--- a/src/gpu/GrClipMaskManager.cpp
+++ b/src/gpu/GrClipMaskManager.cpp
@@ -174,7 +174,9 @@
         if (effect) {
             are->set(fGpu->drawState());
             fGpu->drawState()->addCoverageEffect(effect);
-            fGpu->disableScissor();
+            SkIRect scissorSpaceIBounds(clipSpaceIBounds);
+            scissorSpaceIBounds.offset(-clipDataIn->fOrigin);
+            fGpu->enableScissor(scissorSpaceIBounds);
             this->setGpuStencil();
             return true;
         }