Provide currently_committed_url to PageLoadMetricsObservers

Provide currently_committed_url to PageLoadMetricsObservers

This allows us to track metrics based on where the user is navigating from.
A referer can be used to accomplish this in some cases, though referers
are not always available or may be sanitized to include only the origin
in some cases.

BUG=603948
Review URL: https://codereview.chromium.org/1879413002

Cr-Commit-Position: refs/heads/master@{#387649}
(cherry picked from commit 003fade38f4d89100f517a6469abeb84cd9db165)

Committed: https://chromium.googlesource.com/chromium/src/+/0c2396d866a38f3f3a25f46c332d56cf4c69d67e

[jkarlin, 2016-04-20 13:41:30]

Description was changed from

==========
Provide currently_committed_url to PageLoadMetricsObservers

This allows us to track metrics based on where the user is navigating from.
A referer can be used to accomplish this in some cases, though referers
are not always available or may be sanitized to include only the origin
in some cases.

BUG=603948

Review URL: https://codereview.chromium.org/1879413002

Cr-Commit-Position: refs/heads/master@{#387649}
(cherry picked from commit 003fade38f4d89100f517a6469abeb84cd9db165)
==========

to

==========
Provide currently_committed_url to PageLoadMetricsObservers

This allows us to track metrics based on where the user is navigating from.
A referer can be used to accomplish this in some cases, though referers
are not always available or may be sanitized to include only the origin
in some cases.

BUG=603948

Review URL: https://codereview.chromium.org/1879413002

Cr-Commit-Position: refs/heads/master@{#387649}
(cherry picked from commit 003fade38f4d89100f517a6469abeb84cd9db165)

Committed:
https://chromium.googlesource.com/chromium/src/+/0c2396d866a38f3f3a25f46c332d...
==========

[jkarlin, 2016-04-20 13:41:31]

Committed patchset #1 (id:1) manually as
0c2396d866a38f3f3a25f46c332d56cf4c69d67e.