Update TextSelection for non-user initiated events

This makes Chromium Content API to be able to notify about text
selection changes triggered by non-user events (eg. JavaScript, IME,
autofill).

R=creis@chromium.org,nasko@chromium.org,ekaramad@chromium.org
BUG=671986
TEST=interactive_ui_tests
--gtest_filter=SitePerProcessTextInputManagerTest.NonUserInitiatedTextSelection
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2856093003
Cr-Commit-Position: refs/heads/master@{#473834}
22 files changed