[Mac] Support undo in the omnibox.

chrome/browser/cocoa/autocomplete_text_field_unittest.mm

Index: chrome/browser/cocoa/autocomplete_text_field_unittest.mm
===================================================================
--- chrome/browser/cocoa/autocomplete_text_field_unittest.mm	(revision 31782)
+++ chrome/browser/cocoa/autocomplete_text_field_unittest.mm	(working copy)
@@ -671,6 +671,17 @@
   EXPECT_TRUE([undoManager canUndo]);
   [field_ setAttributedStringValue:attributedString];
   EXPECT_TRUE([undoManager canUndo]);
+
+  // Verify that calling -clearUndoChain clears the undo chain.
+  [field_ clearUndoChain];
+  EXPECT_FALSE([undoManager canUndo]);
 }
 
+TEST_F(AutocompleteTextFieldTest, EditorGetsCorrectUndoManager) {
+  cocoa_helper_.makeFirstResponder(field_);
+
+  NSTextView* editor = static_cast<NSTextView*>([field_ currentEditor]);
+  EXPECT_TRUE(editor);
+  EXPECT_EQ([field_ undoManagerForTextView:editor], [editor undoManager]);
+}
 }  // namespace