Add non-member non-mutating methods for common gfx::Rect operations.

ui/gfx/rect.h

Index: ui/gfx/rect.h
diff --git a/ui/gfx/rect.h b/ui/gfx/rect.h
index 2eab239d4bc76d948c93b86606622841fe778b39..432d77c2f671e708fdb90a0f734b1b86dd789ab4 100644
--- a/ui/gfx/rect.h
+++ b/ui/gfx/rect.h
@@ -75,6 +75,24 @@ inline bool operator!=(const Rect& lhs, const Rect& rhs) {
   return !(lhs == rhs);
 }
 
+inline Rect Intersection(const Rect& a, const Rect& b) {

[sky, 2012/10/25 23:31:53]

I think we need more descriptive names otherwise we can easily conflict. Maybe
IntersectRects. Is there a compelling reason to inline these?

[danakj, 2012/10/26 00:16:04]

Sure, though I thought the same and enne@ convinced me otherwise. Rect does not
implicitly convert to/from anything else, so what would we conflict with?
Nope, other than they are small. Will move to the .cc.

+  Rect result = a;
+  result.Intersect(b);
+  return result;
+}
+
+inline Rect Union(const Rect& a, const Rect& b) {
+  Rect result = a;
+  result.Union(b);
+  return result;
+}
+
+inline Rect Subtraction(const Rect& a, const Rect& b) {
+  Rect result = a;
+  result.Subtract(b);
+  return result;
+}
+
 #if !defined(COMPILER_MSVC)
 extern template class RectBase<Rect, Point, Size, Insets, int>;
 #endif