Add delay to didAssociateFormControlsTimer so it doesn't fire too frequently

When JS iteratively constructs a DOM tree containing form controls, didAssociateFormControlsTimer was fireing for every iteration, causing a massive slow down.

BUG=614856

Review-Url: https://codereview.chromium.org/2055693002
Cr-Commit-Position: refs/heads/master@{#404083}
6 files changed