Reland of Add a NavigationThrottle to the public content/ interface

Reland of Add a NavigationThrottle to the public content/ interface

This CL relands patch https://codereview.chromium.org/1269813002/ that was
reverted because it broke some extension tests on ChromeOS. Original commit
message:

This CL adds a NavigationThrottle class to the public content/ interface. A
NavigationThrottle is used to control the flow of navigations. It lives
entirely on the UI thread. Eventually, all components that want the
functionality of a ResourceThrottle for navigations should transition to a
NavigationThrottle: the new architecture for navigations (browser-side
navigation) will not support ResourceThrottles for main resources load. See
https://docs.google.com/document/d/1ICLLQoC9EsZ-bWH4ZKRhPCIoZKn6pOj02SlGl6SKH6Y/edit?pli=1#heading=h.fmxjmgvbgg7x
for the design doc.

This Cl also transition the InterceptNavigationResourceThrottle to the
NavigationThrottle model.

BUG=504347
TBR=mnaganov@chromium.org, sky@chromium.org, asargent@chromium.org, creis@chromium.org, nasko@chromium.org

Committed: https://crrev.com/40c9e144d4864ee6fa3854e59b322df6107cbe7e
Cr-Commit-Position: refs/heads/master@{#351284}

[clamy, 2015-09-22 22:16:08]

Patchset #2 (id:20001) has been deleted

[clamy, 2015-09-23 01:29:21]

Patchset #2 (id:40001) has been deleted

[clamy, 2015-09-24 18:42:32]

Patchset #2 (id:60001) has been deleted

[clamy, 2015-09-29 09:53:28]

clamy@chromium.org changed reviewers:
+ asargent@chromium.org, creis@chromium.org, mnaganov@chromium.org,
nasko@chromium.org, sky@chromium.org

[clamy, 2015-09-29 09:55:44]

@asargent, creis, mnaganov, nasko, sky: this is a reland of
https://codereview.chromium.org/1269813002/. The original patch exposed a bug in
extension refcounting that was fixed by
https://codereview.chromium.org/1366393002. Since there is no code change in the
reland from the original patch, I'm TBRing you on the review.

[clamy, 2015-09-29 09:55:59]

The CQ bit was checked by clamy@chromium.org

[commit-bot: I haz the power, 2015-09-29 09:56:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1363483007/100001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1363483007/100001

[commit-bot: I haz the power, 2015-09-29 10:38:46]

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

[commit-bot: I haz the power, 2015-09-29 10:38:47]

Try jobs failed on following builders:
  android_clang_dbg_recipe on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)

[clamy, 2015-09-29 10:48:55]

The CQ bit was checked by clamy@chromium.org

[commit-bot: I haz the power, 2015-09-29 10:49:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1363483007/100001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1363483007/100001

[commit-bot: I haz the power, 2015-09-29 11:18:59]

Committed patchset #3 (id:100001)

[commit-bot: I haz the power, 2015-09-29 11:19:52]

Patchset 3 (id:??) landed as
https://crrev.com/40c9e144d4864ee6fa3854e59b322df6107cbe7e
Cr-Commit-Position: refs/heads/master@{#351284}