I added the GN arguments to tools/licenses.py, and it's being actively used by remoting/ on the Android builders. There was one revert which I fixed with _GnBinary(), so I don't think you'll run into any more problems with GN on Android builders.

One thing to be aware of: Chromium has some files under third-party (non-Chromium) copyrights, which don't live under a third_party/ directory. See src/tools/copyright_scanner/third_party_files_whitelist.txt .
This means that tools/licenses.py might not report Credits for these files (but I suppose, neither would cronet_licenses.py). You will want to manually review this whitelist to check that any files pulled in do have Credits reported for them.

This is being discussed on chromium-dev here:
https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/N-MlwA_6CYo

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/997021610f0a7631e4887e999aaacbc9cacbbce8

commit 997021610f0a7631e4887e999aaacbc9cacbbce8
Author: mef <mef@chromium.org>
Date: Thu Jun 29 16:45:18 2017

[Cronet] Replace use of cronet_licenses.py with licenses.py

BUG= 710801 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_cronet_tester

Review-Url: https://codereview.chromium.org/2962963003
Cr-Commit-Position: refs/heads/master@{#483385}

[modify] https://crrev.com/997021610f0a7631e4887e999aaacbc9cacbbce8/components/cronet/ios/BUILD.gn

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0fd5121f8fe912464b4f4d46dbb90d6209f59bf0

commit 0fd5121f8fe912464b4f4d46dbb90d6209f59bf0
Author: mef <mef@chromium.org>
Date: Mon Jul 10 16:30:34 2017

[Cronet] Use gn desc to find third party licenses on Android.

Filter out build/secondary/third_party dependencies to work around
__main__.LicenseError: missing README.chromium or licenses.py SPECIAL_CASES entry in build/secondary/third_party/android_tools

BUG= 606859 
BUG= 710801 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_cronet_tester

Review-Url: https://codereview.chromium.org/2959303002
Cr-Commit-Position: refs/heads/master@{#485291}

[modify] https://crrev.com/0fd5121f8fe912464b4f4d46dbb90d6209f59bf0/components/cronet/android/BUILD.gn
[modify] https://crrev.com/0fd5121f8fe912464b4f4d46dbb90d6209f59bf0/tools/licenses.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/da0a4f9e5cabf886dc27ac4b7dcbd3057a42f248

commit da0a4f9e5cabf886dc27ac4b7dcbd3057a42f248
Author: Misha Efimov <mef@chromium.org>
Date: Thu Jul 20 21:46:04 2017

[Cronet] Remove cronet_licenses.py replaced by common //tools/licenses.py.

Bug:  710801 
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester
Change-Id: I147c082f7ac74ad2bd2843b9c7ca789bac2cec7b
Reviewed-on: https://chromium-review.googlesource.com/579955
Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Misha Efimov <mef@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488420}
[delete] https://crrev.com/13ea31c035bb660596a5d15af2aed54c5e565059/components/cronet/tools/cronet_licenses.py