[Android] Route selection handle dragging updates to ContentViewClient
Notify the ContentViewClient of selection and insertion-related events,
allowing customized behavior depending on the state of selection. This is
particularly relevant for informing how the selection text string is being
updated.
BUG=400824
Review URL: https://codereview.chromium.org/
469483002
Cr-Commit-Position: refs/heads/master@{#289193}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289193 0039d316-1c4b-4281-b951-d872f2087c98