Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl

Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset #3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
>
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
>
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
>
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
Committed: https://crrev.com/268f1bf33d61c34c9ebcb40947f1d262a31ad0b8
Cr-Commit-Position: refs/heads/master@{#375323}

[lazyboy, 2016-02-13 00:15:19]

Created Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl

[lazyboy, 2016-02-13 00:16:56]

Description was changed from

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

TBR=nasko@chromium.org,clamy@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=571887, 298193
==========

to

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

TBR=nasko@chromium.org,clamy@chromium.org
BUG=571887, 298193, 586633
==========

[lazyboy, 2016-02-13 00:17:31]

Description was changed from

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

TBR=nasko@chromium.org,clamy@chromium.org
BUG=571887, 298193, 586633
==========

to

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
==========

[lazyboy, 2016-02-13 00:18:16]

Description was changed from

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
==========

to

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
==========

[lazyboy, 2016-02-13 00:18:26]

The CQ bit was checked by lazyboy@chromium.org

[commit-bot: I haz the power, 2016-02-13 00:18:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1696973002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1696973002/1

[commit-bot: I haz the power, 2016-02-13 01:53:29]

Description was changed from

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
==========

to

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
==========

[commit-bot: I haz the power, 2016-02-13 01:53:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-02-16 22:46:55]

Description was changed from

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
> 
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
> 
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
> 
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633
==========

to

==========
Revert of Reland #1 Remove the is_loading_ field from WebContentsImpl (patchset
#3 id:40001 of https://codereview.chromium.org/1690653003/ )

Reason for revert:
A bunch of SessionHistoryTest.* tests started being flaky on Cast Linux bot
after the CL landed.

See below for details:

Before the CL I've checked 5 builds that never had any failure:
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18670
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18669
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18668
https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18667

After/at the CL a lot of the builds either completely failed and passed on
retry:

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18671
SessionHistoryTest.FrameBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18672
SessionHistoryTest.FragmentBackForward
SessionHistoryTest.HistoryLength

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18677
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18678
SessionHistoryTest.FragmentBackForward

https://build.chromium.org/p/chromium.linux/builders/Cast%20Linux/builds/18679
SessionHistoryTest.BasicBackForward
SessionHistoryTest.HistoryLength

Original issue's description:
> Reland #1 Remove the is_loading_ field from WebContentsImpl
>
> The CL was reverted since it introduced flakyness on the
> SitePerProcessBrowserTest.NavigateRemoteFrameToBlankAndDataURLs test on the
> ChromiumOS dbg bot.
>
> Original commit message:
> This CL removes the is_loading_ field from WebContents, in favor of only
> tracking the loading state through the FrameTree. Currently the loading state
> is tracked in both, leading to more complexity in the code.
>
> BUG=571887, 298193
> TBR=rockot@chromium.org,nick@chromium.org,carlosk@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
TBR=nasko@chromium.org,clamy@chromium.org,rockot@chromium.org
BUG=571887, 298193, 586633

Committed: https://crrev.com/268f1bf33d61c34c9ebcb40947f1d262a31ad0b8
Cr-Commit-Position: refs/heads/master@{#375323}
==========

[commit-bot: I haz the power, 2016-02-16 22:46:56]

Patchset 1 (id:??) landed as
https://crrev.com/268f1bf33d61c34c9ebcb40947f1d262a31ad0b8
Cr-Commit-Position: refs/heads/master@{#375323}