Focus the first/last element when the view is requested for focus by tab traversal.

Focus the first/last element when the view is requested for focus by tab traversal.

In ExtensionDialog, these unexpected behaviors are observed:
 - When the last focusable element has the focus and TAB is pressed, the first focusable element is not focused.
 - When the first focusable element has the focus and Shift+TAB is pressed, the last element is not focused.

This CL fixes these issues by adding the same handling as views::WebView.
https://code.google.com/p/chromium/codesearch#chromium/src/ui/views/controls/webview/webview.cc&q=WebView::AboutToRequestFocusFromTabTraversal&sq=package:chromium&type=cs&l=234

BUG=463030
TEST=run interactive_ui_tests --gtest_filter=ExtensionDialogUiTest.TabFocusLoop

Review URL: https://codereview.chromium.org/994863003

Cr-Commit-Position: refs/heads/master@{#323716}