Fix bug 8369 and another regression

Fixing two small regressions in the Find box:

1) If the Find textfield is populated when the Find box is shown, the FindPrevious and FindNext buttons should also be enabled. (issue 8369)

2) If you search for something that is not on the page, you get "0 of 0" in red. Press Esc and Ctrl+F and the label is gone but the red background color for the label remains (no bug on file, found during testing).

BUG=8369
TEST=Open about:blank in Chrome. Press Ctrl+F, search for 'e' (get 0 of 0), close the Find box, reopen the Find box. Observe 'e' is in box, it is highlighted and no red is visible. Also, FindPrevious and FindNext buttons should be enabled.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=11063