Implement onCompleted event for the webNavigation API

Implement onCompleted event for the webNavigation API

BUG=50943
TEST=browser_tests:*.WebNavigationEvents*

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=65182

[jochen (gone - plz use gerrit), 2010-11-04 12:12:45]

please review

[yzshen, 2010-11-04 17:19:06]

LGTM

Please wait for Matt's comments before submitting.

[Matt Perry, 2010-11-04 18:31:34]

LGTM.

I wonder if we should disable all this navigation tracking if there are no
extensions using the webNavigation API. Probably not worth the effort just for
frame loads, but once we get to the webRequest API we might see an impact.

[jochen (gone - plz use gerrit), 2010-11-04 19:21:53]

On 2010/11/04 18:31:34, Matt Perry wrote:
> LGTM.
> 
> I wonder if we should disable all this navigation tracking if there are no
> extensions using the webNavigation API. Probably not worth the effort just for
> frame loads, but once we get to the webRequest API we might see an impact.

the extension service only forwards events if there's at least one registered
listener. The json data still gets build everytime, so it might be worthwhile
for the web request api to optimize this even further.