Get window origin only once in BrowserToolbarGtk::GetPopupBounds.

This is an optimization, and also helps stability. Fixes an intermittent DCHECK
I was hitting while working on unrelated parts of code.

TEST=There are DCHECKs that make sure the new code is valid.
BUG=none

Review URL: http://codereview.chromium.org/200069

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@25860 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/gtk/browser_toolbar_gtk.cc

@@ -430,16 +430,18 @@ gfx::Rect BrowserToolbarGtk::GetPopupBounds() const {
     right = go_->widget();
   }
 
-  // TODO(deanm): The go and star buttons probably share the same window,
-  // so this could be optimized to only one origin request.
-  gint right_x;
-  gdk_window_get_origin(right->window, &right_x, NULL);
-  right_x += right->allocation.x + right->allocation.width;
-
-  gint left_x, left_y;
-  gdk_window_get_origin(left->window, &left_x, &left_y);
-  left_x += left->allocation.x;
-  left_y += left->allocation.y + left->allocation.height;  // Bottom edge.
+  gint origin_x, origin_y;
+  DCHECK_EQ(left->window, right->window);
+  gdk_window_get_origin(left->window, &origin_x, &origin_y);
+
+  gint right_x = origin_x + right->allocation.x + right->allocation.width;
+
+  gint left_x = origin_x + left->allocation.x;
+
+  // Bottom edge.
+  gint left_y = origin_y + left->allocation.y + left->allocation.height;
+
+  DCHECK_LE(left_x, right_x);
 
   return gfx::Rect(left_x + kPopupLeftRightMargin, left_y + kPopupTopMargin,
                    right_x - left_x - (2 * kPopupLeftRightMargin), 0);