[Android] Redirect obsolete chrome:// URLs to NTP.
When upgrading Chrome from an older version, tabs that are currently
showing chrome://newtab or chrome://welcome will now redirect to the
NTP. Previously, we'd instead show a totally blank page (not even an
error message).
Note: new_tab_page_url_handler.cc has similar logic for redirecting
chrome://newtab and chrome://welcome, but it only affects new
nagivations, not navigations that are restored from serialized tab
state.
BUG=491878
Review URL: https://codereview.chromium.org/
1165613002
Cr-Commit-Position: refs/heads/master@{#332057}