My plan to minimize the number of changes required:

* First change, upstream: add no-Context versions of isGoogleSigned and isChromeGoogleSigned. Make the old isGoogleSigned call the new isGoogleSigned. Make the new isGoogleSigned returns false. This way, the behavior will remain identical in all cases:

- Downstream overrides only the old isGoogleSigned: the override replaces the call to the new isGoogleSigned, so all callers of the old isGoogleSigned get the overridden behavior.

- Downstream overrides only the new isGoogleSigned: the old isGoogleSigned calls the new, overridden isGoogleSigned, so all callers of the old isGoogleSigned get the overridden behavior.

- There is no downstream: isGoogleSigned returns false as usual.

* Second change, downstream: switch isGoogleSigned to override the new version. Switch all downstream callers of isGoogleSigned and isChromeGoogleSigned to the new versions.

* Third change, upstream: remove the old isGoogleSigned and isChromeGoogleSigned. Switch all upstream callers to the new versions.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b728a75415b10f5cf4ca4e1cd1d3cadc615b02d6

commit b728a75415b10f5cf4ca4e1cd1d3cadc615b02d6
Author: paulmiller <paulmiller@chromium.org>
Date: Fri Apr 07 01:34:21 2017

Remove vestigial Context arguments in ExternalAuthUtils, part 1/3

BUG= 709208 

Review-Url: https://codereview.chromium.org/2800013002
Cr-Commit-Position: refs/heads/master@{#462737}

[modify] https://crrev.com/b728a75415b10f5cf4ca4e1cd1d3cadc615b02d6/chrome/android/java/src/org/chromium/chrome/browser/externalauth/ExternalAuthUtils.java

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/clank/internal/apps/+/7f58b09d9500d645007cc71588275175c53ab4c3

commit 7f58b09d9500d645007cc71588275175c53ab4c3
Author: Paul Miller <paulmiller@google.com>
Date: Fri Apr 07 21:45:00 2017

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fd8989730fde1248659628b9a36d74ab421e0040

commit fd8989730fde1248659628b9a36d74ab421e0040
Author: paulmiller <paulmiller@chromium.org>
Date: Fri Apr 07 23:05:01 2017

Remove vestigial Context arguments in ExternalAuthUtils, part 3/3

BUG= 709208 

Review-Url: https://codereview.chromium.org/2806023003
Cr-Commit-Position: refs/heads/master@{#463034}

[modify] https://crrev.com/fd8989730fde1248659628b9a36d74ab421e0040/chrome/android/java/src/org/chromium/chrome/browser/IntentHandler.java
[modify] https://crrev.com/fd8989730fde1248659628b9a36d74ab421e0040/chrome/android/java/src/org/chromium/chrome/browser/externalauth/ExternalAuthUtils.java
[modify] https://crrev.com/fd8989730fde1248659628b9a36d74ab421e0040/chrome/android/java/src/org/chromium/chrome/browser/gcore/ChromeGoogleApiClientImpl.java

Thanks for the clean-up Paul!