Possibly clobbered by changes a while back to limit the number of concurrent tab loads.

NTP pages shows google stuff (doodle, account picture etc). Not sure how it is implemented but I suspect there are traffics to google servers which triggers our MergeSessionLoadPage.

ShouldDelayUrl [1] might be a good start point to investigate. 

[1] https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/chromeos/login/signin/merge_session_throttling_utils.cc&rcl=1456936192&l=170

What is the expected behavior? From what I understood from discussion with Xiyuan, this seems to be necessary to wait until the session is merged.

I think we should load NTP page from local resources only (just if we are offline) instead of blocking it on the signin throttle. It looks super weird that Chrome can't load its "internal" page for 5+ seconds...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/96379036a48ce6ee82040597d5e9b930c21a7a3d

commit 96379036a48ce6ee82040597d5e9b930c21a7a3d
Author: afakhry <afakhry@chromium.org>
Date: Mon Apr 25 18:24:08 2016

Avoid the long merge session throttle interstitial page for NTP on Chrome OS

While the session is being merged, opening the NTP while cause the throttling
interstitial page to kick in, which can cause a delay in displaying the page for
5+ seconds. Instead we should force loading the local NTP until the merge session
is complete.

BUG= 591530 

Review URL: https://codereview.chromium.org/1910693002

Cr-Commit-Position: refs/heads/master@{#389514}

[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_navigation_throttle.cc
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_resource_throttle.cc
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_throttling_utils.cc
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_throttling_utils.h
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/search/search.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/96379036a48ce6ee82040597d5e9b930c21a7a3d

commit 96379036a48ce6ee82040597d5e9b930c21a7a3d
Author: afakhry <afakhry@chromium.org>
Date: Mon Apr 25 18:24:08 2016

Avoid the long merge session throttle interstitial page for NTP on Chrome OS

While the session is being merged, opening the NTP while cause the throttling
interstitial page to kick in, which can cause a delay in displaying the page for
5+ seconds. Instead we should force loading the local NTP until the merge session
is complete.

BUG= 591530 

Review URL: https://codereview.chromium.org/1910693002

Cr-Commit-Position: refs/heads/master@{#389514}

[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_navigation_throttle.cc
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_resource_throttle.cc
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_throttling_utils.cc
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/chromeos/login/signin/merge_session_throttling_utils.h
[modify] https://crrev.com/96379036a48ce6ee82040597d5e9b930c21a7a3d/chrome/browser/search/search.cc

bulk verify (M50 clean up)