Enable using system proxy resolver for android webview.

Android platform provides a local proxy that also handles PAC proxy resolution. The CL below modified enabled chrome network stack to start using V8 proxy resolution on Android platform:
https://codereview.chromium.org/573013002/
however webview cannot use V8 proxy resolution since Webview is significantly different from chrome: Webview is single process vs. chrome is multithreaded and use of V8 isolates creates concurrency problems with Blink's use of V8 isolates.
For now, we want to establish the prior behavior for android webview and consider making changes to v8 proxy resolver in future.

BUG=432539
Committed: https://crrev.com/200b2f027ce820425e37b08ed8b4e5dc84928276
Cr-Commit-Position: refs/heads/master@{#305166}

[sgurun-gerrit only, 2014-11-20 19:52:57]

sgurun@chromium.org changed reviewers:
+ eroman@chromium.org

[sgurun-gerrit only, 2014-11-20 21:41:39]

On 2014/11/20 19:52:57, sgurun wrote:
> mailto:sgurun@chromium.org changed reviewers:
> + mailto:eroman@chromium.org

eroman, PTAL, thanks!

[mnaganov (inactive), 2014-11-20 21:58:35]

mnaganov@chromium.org changed reviewers:
+ mnaganov@chromium.org

[mnaganov (inactive), 2014-11-20 21:58:35]

drive-by style nit

https://codereview.chromium.org/742023003/diff/20001/net/proxy/proxy_config_s...
File net/proxy/proxy_config_service_android.cc (right):

https://codereview.chromium.org/742023003/diff/20001/net/proxy/proxy_config_s...
net/proxy/proxy_config_service_android.cc:275: if (use_local_proxy_)
nit: I think this "if" statement deserves braces for the branches, as one of
them even spans on two lines.

[sgurun-gerrit only, 2014-11-20 23:38:19]

https://codereview.chromium.org/742023003/diff/20001/net/proxy/proxy_config_s...
File net/proxy/proxy_config_service_android.cc (right):

https://codereview.chromium.org/742023003/diff/20001/net/proxy/proxy_config_s...
net/proxy/proxy_config_service_android.cc:275: if (use_local_proxy_)
On 2014/11/20 21:58:35, mnaganov (cr) wrote:
> nit: I think this "if" statement deserves braces for the branches, as one of
> them even spans on two lines.

Done.

[mnaganov (inactive), 2014-11-21 01:25:44]

Thanks! LGTM.

[eroman, 2014-11-21 01:55:15]

Is Chrome on Android using v8 proxy resolver which makes this a non-issue?

The particular mechanism here of "scratching out" the PAC URL and assuming the
provided single-proxy is equivalent is strange (that is not how proxy
configurations work on other platforms).

But if it fixes your issue, then LGTM for now and can iterate on it.

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
File android_webview/browser/aw_browser_context.cc (right):

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
android_webview/browser/aw_browser_context.cc:126:
CreateProxyConfigService()).Pass()));
Should this be a part of net::ProxySerive::CreateSystemProxyConfigService
instead?

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
File android_webview/browser/net/aw_url_request_context_getter.cc (right):

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
android_webview/browser/net/aw_url_request_context_getter.cc:204: // Create
proxy without a resolver since we rely on system proxy resolver.
I don't follow this comment. If no ProxyResolver is passed, then it is not
possible to use the system proxy resolver (since it is through ProxyResolver
that it would interact with either the system proxy resolver or the v8 one).

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
File net/proxy/proxy_config_service_android.cc (right):

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
net/proxy/proxy_config_service_android.cc:287: void set_use_local_proxy(bool
enabled) {
Something like "exclude_pac_url" seems like it would be more fitting. It isn't
clear to me why the reported "host" would be a local url. Is it not possible to
configure a remote proxy?

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
File net/proxy/proxy_config_service_android.h (right):

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
net/proxy/proxy_config_service_android.h:67: // Android provides a local HTTP
proxy that does PAC resolution. When this
I guess this answers my previous question.

[sgurun-gerrit only, 2014-11-21 02:13:37]

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
File android_webview/browser/aw_browser_context.cc (right):

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
android_webview/browser/aw_browser_context.cc:126:
CreateProxyConfigService()).Pass()));
On 2014/11/21 01:55:15, eroman wrote:
> Should this be a part of net::ProxySerive::CreateSystemProxyConfigService
> instead?

I think this is a special case for webview, but I can move it to net in a
subsequent CL if you feel strong about it.

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
File android_webview/browser/net/aw_url_request_context_getter.cc (right):

https://codereview.chromium.org/742023003/diff/40001/android_webview/browser/...
android_webview/browser/net/aw_url_request_context_getter.cc:204: // Create
proxy without a resolver since we rely on system proxy resolver.
On 2014/11/21 01:55:15, eroman wrote:
> I don't follow this comment. If no ProxyResolver is passed, then it is not
> possible to use the system proxy resolver (since it is through ProxyResolver
> that it would interact with either the system proxy resolver or the v8 one).

Himm, there is some background to this. Android provides a local HTTP proxy that
does the proxying. This local HTTP proxy also reflects the PAC setting (if it is
set). Android proxy change intents broadcast the local host/port pair. 

I will update the comments to better explain this.

Because of this trick, PAC was actually working for Android webview in L
release.

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
File net/proxy/proxy_config_service_android.cc (right):

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
net/proxy/proxy_config_service_android.cc:287: void set_use_local_proxy(bool
enabled) {
On 2014/11/21 01:55:15, eroman wrote:
> Something like "exclude_pac_url" seems like it would be more fitting. It isn't
> clear to me why the reported "host" would be a local url. Is it not possible
to
> configure a remote proxy?

Acknowledged. 
I actually think that we are relying on an implementation detail since there is
no SDK guarantee that "host" would always be local. I think we should iterate on
this to have a better support in future.

This change just restores the previous behavior for Android webview.

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
File net/proxy/proxy_config_service_android.h (right):

https://codereview.chromium.org/742023003/diff/40001/net/proxy/proxy_config_s...
net/proxy/proxy_config_service_android.h:67: // Android provides a local HTTP
proxy that does PAC resolution. When this
On 2014/11/21 01:55:15, eroman wrote:
> I guess this answers my previous question.

yes.

[sgurun-gerrit only, 2014-11-21 02:51:43]

The CQ bit was checked by sgurun@chromium.org

[commit-bot: I haz the power, 2014-11-21 02:52:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/742023003/60001

[commit-bot: I haz the power, 2014-11-21 04:42:55]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2014-11-21 04:43:42]

Patchset 4 (id:??) landed as
https://crrev.com/200b2f027ce820425e37b08ed8b4e5dc84928276
Cr-Commit-Position: refs/heads/master@{#305166}

[fujunweitongx, 2016-02-19 01:03:12]

> Himm, there is some background to this. Android provides a local HTTP proxy
that
> does the proxying. This local HTTP proxy also reflects the PAC setting (if it
is
> set). Android proxy change intents broadcast the local host/port pair. 
> 
> I will update the comments to better explain this.
> 
> Because of this trick, PAC was actually working for Android webview in L
> release.

How to use the local proxy to automatically choose the appropriate proxy server
for fetching a given URL?

> Webview is single process vs. chrome is multithreaded and use of V8 isolates 
> creates concurrency problems with Blink's use of V8 isolates. 

I don't understand why this differentiation can't support PAC on Android
platform. Do we have other approaches to implement this feature?