Fix win64 warnings.

TBR=joshualitt@google.com

NOTREECHECKS=true

Review URL: https://codereview.chromium.org/884253004
diff --git a/src/gpu/GrAARectRenderer.cpp b/src/gpu/GrAARectRenderer.cpp
index 6866b79..48692eb 100644
--- a/src/gpu/GrAARectRenderer.cpp
+++ b/src/gpu/GrAARectRenderer.cpp
@@ -227,8 +227,8 @@
     }
 
     void generateAAFillRectGeometry(void* vertices,
-                                    uint32_t offset,
-                                    uint32_t vertexStride,
+                                    size_t offset,
+                                    size_t vertexStride,
                                     GrColor color,
                                     const SkMatrix& viewMatrix,
                                     const SkRect& rect,