fix more 64bit warnings

BUG=skia:

Review URL: https://codereview.chromium.org/147683003

git-svn-id: http://skia.googlecode.com/svn/trunk@13190 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/polygons.cpp b/gm/polygons.cpp
index bddde8f..4360355 100644
--- a/gm/polygons.cpp
+++ b/gm/polygons.cpp
@@ -27,8 +27,8 @@
     }
 
     virtual SkISize onISize() SK_OVERRIDE {
-        size_t width = kNumPolygons * kCellSize + 40;
-        size_t height = (kNumJoins * kNumStrokeWidths + kNumExtraStyles) * kCellSize + 40;
+        int width = kNumPolygons * kCellSize + 40;
+        int height = (kNumJoins * kNumStrokeWidths + kNumExtraStyles) * kCellSize + 40;
         return SkISize::Make(width, height);
     }