Add UMA metrics to measure the dismissal cause of dialogs.

BUG=629964

Review-Url: https://codereview.chromium.org/2535043002
Cr-Commit-Position: refs/heads/master@{#435016}
(cherry picked from commit 70f9ea001b21e3ad255fe0d2bb7822d8e52789b7)

Review URL: https://codereview.chromium.org/2543793003 .

Cr-Commit-Position: refs/branch-heads/2924@{#247}
Cr-Branched-From: 3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}
3 files changed