Fix signed/unsigned comparison warning in PictureTest.cpp



git-svn-id: http://skia.googlecode.com/svn/trunk@7088 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/PictureTest.cpp b/tests/PictureTest.cpp
index d14cf98..26b1f56 100644
--- a/tests/PictureTest.cpp
+++ b/tests/PictureTest.cpp
@@ -130,7 +130,7 @@
             // the color is transparent, meaning no bitmap was drawn in that
             // pixel.
             if (pmc) {
-                int index = SkGetPackedR32(pmc);
+                uint32_t index = SkGetPackedR32(pmc);
                 SkASSERT(SkGetPackedG32(pmc) == index);
                 SkASSERT(SkGetPackedB32(pmc) == index);
                 SkASSERT(index < count);