Improve handling of clip stack ID

Change-Id: I1d5cf06d9b50c370f969a8778181fe94f7d35844
Reviewed-on: https://skia-review.googlesource.com/21061
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/GrReducedClip.cpp b/src/gpu/GrReducedClip.cpp
index dfa4166..e6cea3e 100644
--- a/src/gpu/GrReducedClip.cpp
+++ b/src/gpu/GrReducedClip.cpp
@@ -662,7 +662,7 @@
 
 class StencilClip final : public GrClip {
 public:
-    StencilClip(const SkIRect& scissorRect, int32_t clipStackID)
+    StencilClip(const SkIRect& scissorRect, uint32_t clipStackID)
         : fFixedClip(scissorRect)
         , fClipStackID(clipStackID) {
     }
@@ -694,7 +694,7 @@
     }
 
     GrFixedClip fFixedClip;
-    int32_t     fClipStackID;
+    uint32_t    fClipStackID;
 
     typedef GrClip INHERITED;
 };