Bug 1228314 - added static_cast<int64> in order to avoid overflow. r=seth

MozReview-Commit-ID: KY3qpIlzE5K

--HG--
extra : rebase_source : a716abcb496c9923318f58d21250b6c13182add0

image/SurfaceCache.cpp

@@ -327,7 +327,8 @@ public:
       // Compare sizes. We use an area-based heuristic here instead of computing a
       // truly optimal answer, since it seems very unlikely to make a difference
       // for realistic sizes.
-      int64_t idealArea = idealKey.Size().width * idealKey.Size().height;
+      int64_t idealArea = static_cast<int64_t>(idealKey.Size().width) *
+        static_cast<int64_t>(idealKey.Size().height);
       int64_t surfaceArea = aSurfaceKey.Size().width * aSurfaceKey.Size().height;
       int64_t bestMatchArea =
         bestMatchKey.Size().width * bestMatchKey.Size().height;