[Signin][Android] Reset SigninHelper prefs in SigninHelperTest

This CL adds SigninHelper.resetSharedPrefs calls to SigninHelperTest so
the state doesn't leak between tests. This should fix flaky tests in
this suite.

Bug: 906712
Change-Id: I52afb02a8d9ab94eb859f7539cebd1d171d8e89e
Reviewed-on: https://chromium-review.googlesource.com/c/1365246
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614669}
1 file changed