Pass current value of attributes to WebDOMActivityLogger Setter logs.

Pass the current value of attributes to WebDOMActivityLogger in Setter calls.
In order to keep this clean, separate out log() into logMethod(), logGetter(),
and logSetter().

This is necessary for improvements to the ActivityLogger, where we need to detect if a modification of certain attributes is a switch from a current setting, or an initialization.  In the case of the former, we may need to treat this differently (as it could be modifying to perform ad injection, or other nefarious purposes). 

BUG=356890

Review URL: https://codereview.chromium.org/213783002

git-svn-id: svn://svn.chromium.org/blink/trunk@173227 bbb929c8-8fbe-4397-9dbb-9b2b20218538