Bug 845125. Fix impromper use of CheckedInt.

Previously we're missing the multiplication.

gfx/2d/Blur.cpp

@@ -401,7 +401,7 @@ AlphaBoxBlur::AlphaBoxBlur(const Rect& aRect,
     mStride(aStride),
     mSurfaceAllocationSize(-1)
 {
-  CheckedInt<int32_t> minDataSize = CheckedInt<int32_t>(aRect.width*aRect.height);
+  CheckedInt<int32_t> minDataSize = CheckedInt<int32_t>(aRect.width)*aRect.height;
   if (minDataSize.isValid()) {
     mSurfaceAllocationSize = minDataSize.value();
   }