Reland of Check for already existing entry when adding to SiteProcessMap.

Reland of Check for already existing entry when adding to SiteProcessMap. (patchset #1 id:1 of https://codereview.chromium.org/2749543004/ )

Reason for revert:
Reverting the revert to see if this was indeed the culprit for the flakiness.

Original issue's description:
> Revert of Check for already existing entry when adding to SiteProcessMap. (patchset #7 id:160001 of https://codereview.chromium.org/2739193004/ )
> 
> Reason for revert:
> Speculative revert to see a bot failure.
> 
> SubresourceFilterBrowserTest.FailedProvisionalLoadInMainframe got flaky around this CL, and this is relatively more suspicious in the failing range.
> 
> BUG=701663
> 
> 
> Original issue's description:
> > Check for already existing entry when adding to SiteProcessMap.
> > 
> > The SiteProcessMap::RegisterProcess can overwrite existing entries
> > in the map, which can lead to incorrect process being mapped to
> > a site in process-per-site mode. This CL checks for existence and
> > avoids the overwrite.
> > 
> > BUG=700514
> > CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation
> > 
> > Review-Url: https://codereview.chromium.org/2739193004
> > Cr-Commit-Position: refs/heads/master@{#456920}
> > Committed: https://chromium.googlesource.com/chromium/src/+/0e9d619f88ffabc3c237cbdf75603df8af9925e6
> 
> TBR=creis@chromium.org,rdevlin.cronin@chromium.org,nasko@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=700514
> 
> Review-Url: https://codereview.chromium.org/2749543004
> Cr-Commit-Position: refs/heads/master@{#457010}
> Committed: https://chromium.googlesource.com/chromium/src/+/96bb282f55edfa739e4e5f6633bb5fce61583e87

TBR=creis@chromium.org,rdevlin.cronin@chromium.org,tzik@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=701663
Review-Url: https://codereview.chromium.org/2755643003
Cr-Commit-Position: refs/heads/master@{#457110}
Committed: https://chromium.googlesource.com/chromium/src/+/0bcbed7d67f9a2813e1a278aada6c047a26bbbff

[nasko, 2017-03-15 17:01:10]

The CQ bit was checked by nasko@chromium.org

[nasko, 2017-03-15 17:01:11]

Created Reland of Check for already existing entry when adding to
SiteProcessMap.

[commit-bot: I haz the power, 2017-03-15 17:01:34]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-15 17:03:42]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1489597270820950, "parent_rev":
"e5394bb17d12ce01acf000f5017be4c4c28ff83c", "commit_rev":
"0bcbed7d67f9a2813e1a278aada6c047a26bbbff"}

[commit-bot: I haz the power, 2017-03-15 17:04:25]

Description was changed from

==========
Reland of Check for already existing entry when adding to SiteProcessMap.
(patchset #1 id:1 of https://codereview.chromium.org/2749543004/ )

Reason for revert:
Reverting the revert to see if this was indeed the culprit for the flakiness.

Original issue's description:
> Revert of Check for already existing entry when adding to SiteProcessMap.
(patchset #7 id:160001 of https://codereview.chromium.org/2739193004/ )
> 
> Reason for revert:
> Speculative revert to see a bot failure.
> 
> SubresourceFilterBrowserTest.FailedProvisionalLoadInMainframe got flaky around
this CL, and this is relatively more suspicious in the failing range.
> 
> BUG=701663
> 
> 
> Original issue's description:
> > Check for already existing entry when adding to SiteProcessMap.
> > 
> > The SiteProcessMap::RegisterProcess can overwrite existing entries
> > in the map, which can lead to incorrect process being mapped to
> > a site in process-per-site mode. This CL checks for existence and
> > avoids the overwrite.
> > 
> > BUG=700514
> > CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation
> > 
> > Review-Url: https://codereview.chromium.org/2739193004
> > Cr-Commit-Position: refs/heads/master@{#456920}
> > Committed:
https://chromium.googlesource.com/chromium/src/+/0e9d619f88ffabc3c237cbdf7560...
> 
> TBR=creis@chromium.org,rdevlin.cronin@chromium.org,nasko@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=700514
> 
> Review-Url: https://codereview.chromium.org/2749543004
> Cr-Commit-Position: refs/heads/master@{#457010}
> Committed:
https://chromium.googlesource.com/chromium/src/+/96bb282f55edfa739e4e5f6633bb...

TBR=creis@chromium.org,rdevlin.cronin@chromium.org,tzik@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=701663
==========

to

==========
Reland of Check for already existing entry when adding to SiteProcessMap.
(patchset #1 id:1 of https://codereview.chromium.org/2749543004/ )

Reason for revert:
Reverting the revert to see if this was indeed the culprit for the flakiness.

Original issue's description:
> Revert of Check for already existing entry when adding to SiteProcessMap.
(patchset #7 id:160001 of https://codereview.chromium.org/2739193004/ )
> 
> Reason for revert:
> Speculative revert to see a bot failure.
> 
> SubresourceFilterBrowserTest.FailedProvisionalLoadInMainframe got flaky around
this CL, and this is relatively more suspicious in the failing range.
> 
> BUG=701663
> 
> 
> Original issue's description:
> > Check for already existing entry when adding to SiteProcessMap.
> > 
> > The SiteProcessMap::RegisterProcess can overwrite existing entries
> > in the map, which can lead to incorrect process being mapped to
> > a site in process-per-site mode. This CL checks for existence and
> > avoids the overwrite.
> > 
> > BUG=700514
> > CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation
> > 
> > Review-Url: https://codereview.chromium.org/2739193004
> > Cr-Commit-Position: refs/heads/master@{#456920}
> > Committed:
https://chromium.googlesource.com/chromium/src/+/0e9d619f88ffabc3c237cbdf7560...
> 
> TBR=creis@chromium.org,rdevlin.cronin@chromium.org,nasko@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=700514
> 
> Review-Url: https://codereview.chromium.org/2749543004
> Cr-Commit-Position: refs/heads/master@{#457010}
> Committed:
https://chromium.googlesource.com/chromium/src/+/96bb282f55edfa739e4e5f6633bb...

TBR=creis@chromium.org,rdevlin.cronin@chromium.org,tzik@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=701663

Review-Url: https://codereview.chromium.org/2755643003
Cr-Commit-Position: refs/heads/master@{#457110}
Committed:
https://chromium.googlesource.com/chromium/src/+/0bcbed7d67f9a2813e1a278aada6...
==========

[commit-bot: I haz the power, 2017-03-15 17:04:26]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/0bcbed7d67f9a2813e1a278aada6...

[nasko, 2017-03-15 21:16:51]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2756573002/ by nasko@chromium.org.

The reason for reverting is: Test is flaking again, reverting the reland..