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}
(cherry picked from commit 0c254feb3c58b5a9223591084e77d093173d582b)

Review URL: https://codereview.chromium.org/2305923003 .

Cr-Commit-Position: refs/branch-heads/2785@{#816}
Cr-Branched-From: 68623971be0cfc492a2cb0427d7f478e7b214c24-refs/heads/master@{#403382}
1 file changed