[signin] Remove dependency of IOSWebViewSigninClient on SigninErrorController

SigninClient implementations should not depend on SigninErrorController.
The dependency should be the other way around.
This CL fixes the WebView implementation of SigninClient.

NOTRY=true

Change-Id: I0592028bd988036bc01a2a48d375337f077bfbd7
Bug: 836212
Reviewed-on: https://chromium-review.googlesource.com/c/1348035
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611090}
7 files changed