small fix for clip mask cache clear

src/gpu/GrDrawTarget.h

Index: src/gpu/GrDrawTarget.h
diff --git a/src/gpu/GrDrawTarget.h b/src/gpu/GrDrawTarget.h
index 1f26166f6e9f96ddc66cc744f0346727b1001c61..7d8a03ce718836caf1c507af32a1a34aa347e2d6 100644
--- a/src/gpu/GrDrawTarget.h
+++ b/src/gpu/GrDrawTarget.h
@@ -968,6 +968,16 @@ public:
      */
     virtual void clearStencilClip(const SkIRect& rect, bool insideClip, GrRenderTarget* = NULL) = 0;
 
+    /**
+     * Release any resources that are cached but not currently in use. This
+     * is intended to give an application some recourse when resources are low.
+     */
+    virtual void purgeResources() SK_OVERRIDE {
+        // The clip mask manager can rebuild all its clip masks so just
+        // get rid of them all.
+        fClipMaskManager.purgeResources();
+    };
+
 protected:
     GrClipMaskManager           fClipMaskManager;