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/2316373005 .

Cr-Commit-Position: refs/branch-heads/2840@{#244}
Cr-Branched-From: 1ae106dbab4bddd85132d5b75c670794311f4c57-refs/heads/master@{#414607}
1 file changed