Remove isSyncDatabase in WebDatabaseObserver [1/3]

This patch duplicates some methods without the unneccessary
parameter in order to switch to using them in the following patch.

[1] THIS PATCH
[2] https://codereview.chromium.org/666333002/
[3] https://codereview.chromium.org/669063002/

BUG=428254

Review URL: https://codereview.chromium.org/660873004

git-svn-id: svn://svn.chromium.org/blink/trunk@184661 bbb929c8-8fbe-4397-9dbb-9b2b20218538