fix memory leak

TBR=
BUG=skia:

Review URL: https://codereview.chromium.org/668333005
diff --git a/src/gpu/GrOvalRenderer.cpp b/src/gpu/GrOvalRenderer.cpp
index 0622994..8c3b99c 100644
--- a/src/gpu/GrOvalRenderer.cpp
+++ b/src/gpu/GrOvalRenderer.cpp
@@ -460,6 +460,7 @@
 
 void GrOvalRenderer::reset() {
     SkSafeSetNull(fRRectIndexBuffer);
+    SkSafeSetNull(fStrokeRRectIndexBuffer);
 }
 
 bool GrOvalRenderer::drawOval(GrDrawTarget* target, const GrContext* context, bool useAA,