Make GTK file dialog box modal for parent window, instead of for the entire...

Make GTK file dialog box modal for parent window, instead of for the entire
application.

This works by adding the GtkWindow in BrowserWindowGtk to its own
GtkWindowGroup and adding the SelectFile dialog to the same group. The
following call to gtk_grab_add(...) makes the SelectFile dialog modal, but
only to the windows within the same group.

Similarly, the bookmark manager window is also added to its own unique
GtkWindowGroup, so the import/export dialogs behave correctly.

If I'm understanding things correctly, the GtkWindowGroup objects are
reference counted once the have windows attached to them, and will delete
themselves after all references to them are destroyed. I'm not sure how to
verify this.

Test:

- Open two new chrome window: A and B
- Open "Save file as..." dialog in window A
- Verify that window A does not respond to keyboard or mouse events.
- Verify that window B does responde to keyboard and mouse events.
- Open "Save file as..." dialog in window B
- Verify that window B does not respond to keyboard or mouse events.
- Cancel dialog on window A.
- Verify that window A starts responding to keyboard and mouse events.
- Cancel dialog on window B.
- Verify that window B starts responding to keyboard and mouse events.

BUG=8727
patch by Mohit Muthanna <mmuthanna@google.com>;
original review URL: http://codereview.chromium.org/149548


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=20667