Inline CharacterData::checkCharDataOperation into the call sites

The number of lines this method adds to each caller, and the method itself, doesn't
justify it existing. It just makes the code harder to follow since it's not obvious
what exception each of these methods can throw.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/21077004

git-svn-id: svn://svn.chromium.org/blink/trunk@155144 bbb929c8-8fbe-4397-9dbb-9b2b20218538