[DevTools] Use main frame when searching/creating DevToolsAgentHost.

[DevTools] Use main frame when searching/creating DevToolsAgentHost.

It was possible to create DTAH for cross-process child frame and
then get it back when asking for WebContents' DTAH.
Instead, we go for main frame explicitly.

This bug only manifested with context menu on cross-process iframe, since
we have both per-WebContents and per-frame methods. Ideally, we'd use
either one or another, but we need per-frame one now, while per-WebContents
is the way to go when cross-process frames would be inspected in the same
DevTools window.

BUG=598005
TEST=SitePerProcessDevToolsBrowserTest.AgentHostForPageEqualsOneForMainFrame

Committed: https://crrev.com/0fe3f402fe308f7b34317be38590d23bad3c84bc
Cr-Commit-Position: refs/heads/master@{#383646}

[dgozman, 2016-03-28 19:27:55]

dgozman@chromium.org changed reviewers:
+ pfeldman@chromium.org

[dgozman, 2016-03-28 19:27:56]

Could you please take a look?

[pfeldman, 2016-03-29 00:25:31]

lgtm

[dgozman, 2016-03-29 00:25:57]

The CQ bit was checked by dgozman@chromium.org

[commit-bot: I haz the power, 2016-03-29 00:26:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1835943003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1835943003/1

[commit-bot: I haz the power, 2016-03-29 01:25:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-29 01:26:17]

Description was changed from

==========
[DevTools] Use main frame when searching/creating DevToolsAgentHost.

It was possible to create DTAH for cross-process child frame and
then get it back when asking for WebContents' DTAH.
Instead, we go for main frame explicitly.

This bug only manifested with context menu on cross-process iframe, since
we have both per-WebContents and per-frame methods. Ideally, we'd use
either one or another, but we need per-frame one now, while per-WebContents
is the way to go when cross-process frames would be inspected in the same
DevTools window.

BUG=598005
TEST=SitePerProcessDevToolsBrowserTest.AgentHostForPageEqualsOneForMainFrame
==========

to

==========
[DevTools] Use main frame when searching/creating DevToolsAgentHost.

It was possible to create DTAH for cross-process child frame and
then get it back when asking for WebContents' DTAH.
Instead, we go for main frame explicitly.

This bug only manifested with context menu on cross-process iframe, since
we have both per-WebContents and per-frame methods. Ideally, we'd use
either one or another, but we need per-frame one now, while per-WebContents
is the way to go when cross-process frames would be inspected in the same
DevTools window.

BUG=598005
TEST=SitePerProcessDevToolsBrowserTest.AgentHostForPageEqualsOneForMainFrame

Committed: https://crrev.com/0fe3f402fe308f7b34317be38590d23bad3c84bc
Cr-Commit-Position: refs/heads/master@{#383646}
==========

[commit-bot: I haz the power, 2016-03-29 01:26:18]

Patchset 1 (id:??) landed as
https://crrev.com/0fe3f402fe308f7b34317be38590d23bad3c84bc
Cr-Commit-Position: refs/heads/master@{#383646}