Prune shared extendion module after extension updating.

Prune shared extension module after extension updating.

When an extension is updated, the imported module of the extension could be changed in the new version. If the imported modules are removed in the new version, we need check and remove the shared modules if necessary.

BUG=393232
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283574

[Peng, 2014-07-11 16:30:48]

PTAL. Thanks.

[asargent_no_longer_on_chrome, 2014-07-11 20:58:28]

It seems like it would be a lot simpler if, any time an extension is uninstalled
or updated, we just checked all shared modules if they are still referenced by
anyone instead of having this special purpose code.

Given that most users have a relatively small number (< 20) extensions/apps
installed, and furthermore uninstalls/updates don't happen all that often, it
doesn't seem like this would be that expensive. Thoughts?

[Peng, 2014-07-14 20:53:49]

PTAL. Thanks.

[Peng, 2014-07-14 21:07:27]

+rlp@chromium.org for chrome/browser/search/*
+tzik@chromium.org for chrome/browser/sync_file_system/*
+pavely@chromium.org for chrome/browser/sync/*

[tzik, 2014-07-15 01:28:56]

sync_file_system/ changes lgtm

[pavely, 2014-07-15 16:59:37]

chrome/browser/sync/* lgtm

[rpetterson, 2014-07-15 19:53:22]

On 2014/07/15 16:59:37, pavely wrote:
> chrome/browser/sync/* lgtm

chrome/browser/search/hotword* lgtm

[asargent_no_longer_on_chrome, 2014-07-16 18:59:27]

lgtm

[Peng, 2014-07-16 19:03:14]

The CQ bit was checked by penghuang@chromium.org

[commit-bot: I haz the power, 2014-07-16 19:06:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/penghuang@chromium.org/386033002/60001

[commit-bot: I haz the power, 2014-07-16 23:27:54]

Change committed as 283574