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/tests/ClipStackTest.cpp b/tests/ClipStackTest.cpp
index af57f9e..e1aa148 100644
--- a/tests/ClipStackTest.cpp
+++ b/tests/ClipStackTest.cpp
@@ -1107,16 +1107,16 @@
 
         stack.clipRect(SkRect::MakeXYWH(0, 0, SkScalar(25.3), SkScalar(25.3)), SkMatrix::I(),
                        kReplace_SkClipOp, true);
-        int32_t genIDA = stack.getTopmostGenID();
+        uint32_t genIDA = stack.getTopmostGenID();
         stack.clipRect(SkRect::MakeXYWH(50, 0, SkScalar(25.3), SkScalar(25.3)), SkMatrix::I(),
                        kUnion_SkClipOp, true);
-        int32_t genIDB = stack.getTopmostGenID();
+        uint32_t genIDB = stack.getTopmostGenID();
         stack.clipRect(SkRect::MakeXYWH(0, 50, SkScalar(25.3), SkScalar(25.3)), SkMatrix::I(),
                        kUnion_SkClipOp, true);
-        int32_t genIDC = stack.getTopmostGenID();
+        uint32_t genIDC = stack.getTopmostGenID();
         stack.clipRect(SkRect::MakeXYWH(50, 50, SkScalar(25.3), SkScalar(25.3)), SkMatrix::I(),
                        kUnion_SkClipOp, true);
-        int32_t genIDD = stack.getTopmostGenID();
+        uint32_t genIDD = stack.getTopmostGenID();
 
 
 #define IXYWH SkIRect::MakeXYWH
@@ -1135,7 +1135,7 @@
         static const struct SUPPRESS_VISIBILITY_WARNING {
             SkRect testBounds;
             int reducedClipCount;
-            int32_t reducedGenID;
+            uint32_t reducedGenID;
             InitialState initialState;
             SkIRect clipIRect;
             // parameter.