Linux: Attempt #2 at updating PRIMARY selection on Ctrl-C in omnibox.

Linux: Attempt #2 at updating PRIMARY selection on Ctrl-C in omnibox.

r23596 was the original attempt; r23714 reverted it.  Using
gtk_text_buffer_copy_clipboard() gives the GtkTextBuffer
ownership of the GtkClipboard and appears to prevent it from 
unhighlighting its text.

Tested as follows:
1. Select text in webkit and hit Ctrl-C; check that both the
   PRIMARY and CLIPBOARD selections contain it.
2. Click in the omnibox.  All of the text gets highlighted.  
   Check that the PRIMARY selection contains the omnibox text and
   the CLIPBOARD selection contains the webkit text.
3. Type Ctrl-C and confirm that the CLIPBOARD selection now 
   contains the omnibox text.
4. Copy webkit text back to both selections.
5. Type Ctrl-L.  The omnibox text gets highlighted but both 
   selections still contain the webkit text.
6. Type Ctrl-C and confirm that both selections now contain the 
   omnibox text.
7. Try hitting Ctrl-C again while the omnibox text is on the 
   CLIPBOARD selection to make sure that a bizarre GTK crash 
   doesn't occur (see comment in code).

BUG=19648
TESTED=see above

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=23834

[Evan Stade, 2009-08-19 23:44:05]

ok

[Dean McNamee, 2009-08-20 17:59:13]

okay