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This is a re-land of https://codereview.chromium.org/1126383005, fixed
not to cause a crash when 'WebView.loadUrl' is called from inside the
onReceivedTitle callback, added a regression test. Also, the document
title is now cached to minimize the amount of callback calls.

Original patch description:

The usual channel for delivering onReceivedTitle (via updating title for
a NavigationEntry) doesn't work in the case of history navigations, because
WebContentsImpl silences no-op updates of entries titles.

Chrome Browser uses another event for updating the title in this case --
via WebContentsDelegate::LoadingStateChanged. This patch enables WebView to
use it as well.

Note that WebChromeClient.onReceivedIcon doesn't need to be re-sent, as
nobody seems to bother checking whether the icon update is a "no-op", so
updates on history navigations just work.

BUG=481570,495234

Review URL: https://codereview.chromium.org/1161783005

Cr-Commit-Position: refs/heads/master@{#333056}