fix warnings
Review URL: https://codereview.appspot.com/7073044

git-svn-id: http://skia.googlecode.com/svn/trunk@7064 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkDeferredCanvas.cpp b/src/utils/SkDeferredCanvas.cpp
index a1e32bc..26ac088 100644
--- a/src/utils/SkDeferredCanvas.cpp
+++ b/src/utils/SkDeferredCanvas.cpp
@@ -20,7 +20,7 @@
 enum {
     // Deferred canvas will auto-flush when recording reaches this limit
     kDefaultMaxRecordingStorageBytes = 64*1024*1024,
-    kDeferredCanvasBitmapSizeThreshold = ~0, // Disables this feature
+    kDeferredCanvasBitmapSizeThreshold = ~0U, // Disables this feature
 };
 
 enum PlaybackMode {