Implement Platform::getUniqueIdForProcess.

Implement Platform::getUniqueIdForProcess.

BUG=501069, 499332
Committed: https://crrev.com/f5f91f945f8c03393460d7375f8837078f50cf85
Cr-Commit-Position: refs/heads/master@{#335801}

[rickyz (no longer on Chrome), 2015-06-22 21:19:24]

rickyz@chromium.org changed reviewers:
+ jln@chromium.org, jochen@chromium.org

[rickyz (no longer on Chrome), 2015-06-22 21:19:25]

Hey, here's the chromium side of the change to expose a unique id for processes
to blink. As a temporary measure, I'm grabbing the PID outside the PID ns from
TraceLog, though this can be replaced by base::GetUniqueIdForProcess once that's
in.

[jochen (gone - plz use gerrit), 2015-06-23 14:53:17]

can you please also add this to components/html_viewer/blink_platform_impl.cc?

lgtm with that

[rickyz (no longer on Chrome), 2015-06-23 21:44:53]

The CQ bit was checked by rickyz@chromium.org

[rickyz (no longer on Chrome), 2015-06-23 21:44:53]

The patchset sent to the CQ was uploaded after l-g-t-m from jochen@chromium.org
Link to the patchset: https://codereview.chromium.org/1186933004/#ps20001
(title: "Add to components/html_viewer/blink_platform_impl.cc")

[commit-bot: I haz the power, 2015-06-23 21:47:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1186933004/20001

[commit-bot: I haz the power, 2015-06-23 22:42:01]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-23 22:42:03]

Exceeded global retry quota

[rickyz (no longer on Chrome), 2015-06-23 23:04:42]

The CQ bit was checked by rickyz@chromium.org

[commit-bot: I haz the power, 2015-06-23 23:06:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1186933004/20001

[commit-bot: I haz the power, 2015-06-23 23:20:31]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-23 23:22:28]

Patchset 2 (id:??) landed as
https://crrev.com/f5f91f945f8c03393460d7375f8837078f50cf85
Cr-Commit-Position: refs/heads/master@{#335801}