Enable untrusted mousedown on select boxes for webview

We have found that some webviews are using fastclick inside them and
due to a risk of breakage we are going to allow mousedown on selects
even if they are untrusted.

BUG=642698

Review-Url: https://codereview.chromium.org/2300633007
Cr-Commit-Position: refs/heads/master@{#416330}
1 file changed