Merge to 2743 "[DevTools] Explicitly reset context group when clearing ScriptController."

Merge to 2743 "[DevTools] Explicitly reset context group when clearing ScriptController."
> [DevTools] Explicitly reset context group when clearing ScriptController.
>
> Previously, we assumed that main world context creation means reset.
> This is not the case when content script is executed before main world script,
> and we ended up with content script context being cleared from debugger.
> Now we get explicit notification from ScriptController to reset (mainly on navigation).
>
> BUG=617530
>
> Review-Url: https://codereview.chromium.org/2064133002
> Cr-Commit-Position: refs/heads/master@{#400770}
(cherry picked from commit 151d5d907870e262ff7f94fd4b1f1e5ef887e96d)
TBR=pfeldman@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/87c1e7416fb66c6892abb38d9295c611e03e1157

[dgozman, 2016-06-28 17:24:49]

Description was changed from

==========
Merge to 2743 "[DevTools] Explicitly reset context group when clearing
ScriptController."
> [DevTools] Explicitly reset context group when clearing ScriptController.
>
> Previously, we assumed that main world context creation means reset.
> This is not the case when content script is executed before main world script,
> and we ended up with content script context being cleared from debugger.
> Now we get explicit notification from ScriptController to reset (mainly on
navigation).
>
> BUG=617530
>
> Review-Url: https://codereview.chromium.org/2064133002
> Cr-Commit-Position: refs/heads/master@{#400770}
(cherry picked from commit 151d5d907870e262ff7f94fd4b1f1e5ef887e96d)
TBR=pfeldman@chromium.org
==========

to

==========
Merge to 2743 "[DevTools] Explicitly reset context group when clearing
ScriptController."
> [DevTools] Explicitly reset context group when clearing ScriptController.
>
> Previously, we assumed that main world context creation means reset.
> This is not the case when content script is executed before main world script,
> and we ended up with content script context being cleared from debugger.
> Now we get explicit notification from ScriptController to reset (mainly on
navigation).
>
> BUG=617530
>
> Review-Url: https://codereview.chromium.org/2064133002
> Cr-Commit-Position: refs/heads/master@{#400770}
(cherry picked from commit 151d5d907870e262ff7f94fd4b1f1e5ef887e96d)
TBR=pfeldman@chromium.org

Committed:
https://chromium.googlesource.com/chromium/src/+/87c1e7416fb66c6892abb38d9295...
==========

[dgozman, 2016-06-28 17:24:51]

Committed patchset #1 (id:1) manually as
87c1e7416fb66c6892abb38d9295c611e03e1157.