[Mac] Support option-return to open in new foreground tab.

BUG=http://crbug.com/22882
TEST=Type something into the omnibox.  Option-return should open it in a new foreground tab.
TEST=After using Option-return to open something in a new foreground tab, switch back to the original tab and verify that the url in the omnibox has reverted to the original page's url.
TEST=Option-leftclick on a link in a webpage should still prompt you to "save as."
Review URL: http://codereview.chromium.org/218032

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@27127 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/autocomplete/autocomplete_edit_view_mac.mm

@@ -804,9 +804,9 @@ std::wstring AutocompleteEditViewMac::GetClipboardText(Clipboard* clipboard) {
     return YES;
   }
 
-  // TODO(shess): Option-return, would normally insert a literal
-  // newline.  Consider combining with -insertNewline:.
+  // Option-Return
   if (cmd == @selector(insertNewlineIgnoringFieldEditor:)) {
+    edit_view_->AcceptInput(NEW_FOREGROUND_TAB, false);
     return YES;
   }