Move SigninErrorController out of signin_internals target

After https://chromium-review.googlesource.com/c/chromium/src/+/1390012,
SigninErrorController is now layered on top of signin internals code
rather than being part of it. This CL accordingly move it out of the
signin_internals GN target back into the browser target that is layered
on top of it.

I verified that making this change did not remove any dependencies from
the signin_internals target (that would have been a nice side-benefit).

Bug: 917836
Change-Id: I5dc4947722c6183c91d3cee3225404919bd4b21a
Reviewed-on: https://chromium-review.googlesource.com/c/1391671Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619901}

components/signin/core/browser/BUILD.gn

@@ -68,8 +68,6 @@ static_library("internals") {
     "profile_oauth2_token_service.h",
     "signin_client.cc",
     "signin_client.h",
-    "signin_error_controller.cc",
-    "signin_error_controller.h",
     "signin_internals_util.cc",
     "signin_internals_util.h",
     "signin_manager.cc",
@@ -133,6 +131,8 @@ static_library("browser") {
     "dice_header_helper.h",
     "mirror_account_reconcilor_delegate.cc",
     "mirror_account_reconcilor_delegate.h",
+    "signin_error_controller.cc",
+    "signin_error_controller.h",
     "signin_header_helper.cc",
     "signin_header_helper.h",
     "signin_investigator.cc",