Password Manager should not clean cached passwords on in-page navigation

Some pages (e.g., twitter) do strange main-frame navigation just before submitting a form. We need to prevent this clearing the cached forms. We do this by only clearing the forms if the navigation is not in-page.

This is an alternative solution to https://codereview.chromium.org/40383002/.

BUG=291291, 278130

Review URL: https://codereview.chromium.org/50893002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232094 0039d316-1c4b-4281-b951-d872f2087c98
Disabling DevToolsSanityTest.TestBeforeUnloadEvents on Win
DevToolsSanityTest.TestBeforeUnloadEvents is flaky on Win Aura.

TBR=yurys@chromium.org
NOTRY=true
BUG=313658

Review URL: https://codereview.chromium.org/54103003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232095 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232095