Add a subtle reminder that chrome_extensions.js is overwritten.

Add a subtle reminder that chrome_extensions.js is overwritten.

Also update from github in the process. Leaves externs currently pending
review as parts of Chrome already rely on them.

R=tbreisacher@chromium.org,hirono@chromium.org
BUG=none

Committed: https://crrev.com/b997d1d058fbb5ef0e70c2416e4e9a6d72b74bdf
Cr-Commit-Position: refs/heads/master@{#322471}

[Dan Beam, 2015-03-26 00:38:01]

dbeam@chromium.org changed reviewers:
+ hirono@chromium.org

[Dan Beam, 2015-03-26 00:38:10]

Patchset #2 (id:20001) has been deleted

[Dan Beam, 2015-03-26 00:38:14]

Patchset #1 (id:1) has been deleted

[Dan Beam, 2015-03-26 00:38:32]

also TBR=hirono@ for small compile fix in ui/file_manager

[Tyler Breisacher (Chromium), 2015-03-26 04:17:31]

lgtm

[hirono, 2015-03-26 13:02:07]

On 2015/03/26 04:17:31, Tyler Breisacher (Chromium) wrote:
> lgtm

lg

[hirono, 2015-03-26 13:02:16]

On 2015/03/26 13:02:07, hirono wrote:
> On 2015/03/26 04:17:31, Tyler Breisacher (Chromium) wrote:
> > lgtm
> 
> lg

lgtm!

[Dan Beam, 2015-03-26 20:31:16]

The CQ bit was checked by dbeam@chromium.org

[commit-bot: I haz the power, 2015-03-26 20:32:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1034873002/60001

[commit-bot: I haz the power, 2015-03-26 21:14:35]

Committed patchset #2 (id:60001)

[commit-bot: I haz the power, 2015-03-26 21:15:55]

Patchset 2 (id:??) landed as
https://crrev.com/b997d1d058fbb5ef0e70c2416e4e9a6d72b74bdf
Cr-Commit-Position: refs/heads/master@{#322471}