Converts BaseView to be non-opaque, which will fix drawing of...

chrome/browser/tab_contents/tab_contents_view_mac.mm

Index: chrome/browser/tab_contents/tab_contents_view_mac.mm
===================================================================
--- chrome/browser/tab_contents/tab_contents_view_mac.mm	(revision 19556)
+++ chrome/browser/tab_contents/tab_contents_view_mac.mm	(working copy)
@@ -261,6 +261,16 @@
   }
 }
 
+- (BOOL)mouseDownCanMoveWindow {
+  // This is needed to prevent mouseDowns from moving the window
+  // around.  The default implementation returns YES only for opaque
+  // views.  TabContentsViewCocoa does not draw itself in any way, but
+  // its subviews do paint their entire frames.  Returning NO here
+  // saves us the effort of overriding this method in every possible
+  // subview.
+  return NO;
+}
+
 // In the Windows version, we always have cut/copy/paste enabled. This is sub-
 // optimal, but we do it too. TODO(avi): Plumb the "can*" methods up from
 // WebCore.