TEMPORARY: track stencil clip state in GrRenderTargetOpList

Tracks the stencil clip state in GrRenderTargetOpList instead of
GrStencilAttachment. This is a temporary move to unblock MDB, after
which point we will be able to overhaul clipping.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2468743002

Review-Url: https://codereview.chromium.org/2468743002
diff --git a/src/gpu/GrRenderTargetOpList.h b/src/gpu/GrRenderTargetOpList.h
index 2a7f1a1..e4b2bf6 100644
--- a/src/gpu/GrRenderTargetOpList.h
+++ b/src/gpu/GrRenderTargetOpList.h
@@ -131,7 +131,7 @@
     SkDEBUGCODE(void dump() const override;)
 
 private:
-    friend class GrRenderTargetContextPriv; // for clearStencilClip
+    friend class GrRenderTargetContextPriv; // for clearStencilClip and stencil clip state.
 
     // Returns the batch that the input batch was combined with or the input batch if it wasn't
     // combined.
@@ -169,6 +169,10 @@
 
     SkAutoTDelete<gr_instanced::InstancedRendering> fInstancedRendering;
 
+    int32_t                                         fLastClipStackGenID;
+    SkIRect                                         fLastClipStackRect;
+    SkIPoint                                        fLastClipOrigin;
+
     typedef GrOpList INHERITED;
 };