Revert of Revert "gclient: Change the .gclient URL mismatch warning into an error." (https://codereview.chromium.org/213483003/)

Reason for revert:
Re-landing this after https://codereview.chromium.org/214813002/

Original issue's description:
> Revert "gclient: Change the .gclient URL mismatch warning into an error."
> 
> This reverts commit c01bff7518.
> 
> BUG=356881
> TBR=iannucci
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=259727

TBR=iannucci@chromium.org,smut@google.com
NOTREECHECKS=true
NOTRY=true
BUG=356881

Review URL: https://codereview.chromium.org/221423004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@261158 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -1053,14 +1053,9 @@ solutions = [
         scm = gclient_scm.CreateSCM(dep.url, self.root_dir, dep.name)
         actual_url = scm.GetActualRemoteURL()
         if actual_url and not scm.DoesRemoteURLMatch():
-          gclient_utils.AddWarning('''
-################################################################################
-################################### WARNING! ###################################
-################################################################################
-
+          raise gclient_utils.Error('''
 Your .gclient file seems to be broken. The requested URL is different from what
-is actually checked out in %(checkout_path)s. In the future this will be an
-error.
+is actually checked out in %(checkout_path)s.
 
 Expected: %(expected_url)s (%(expected_scm)s)
 Actual:   %(actual_url)s (%(actual_scm)s)
@@ -1069,10 +1064,6 @@ You should ensure that the URL listed in .gclient is correct and either change
 it or fix the checkout. If you're managing your own git checkout in
 %(checkout_path)s but the URL in .gclient is for an svn repository, you probably
 want to set 'managed': False in .gclient.
-
-################################################################################
-################################################################################
-################################################################################
 '''  % {'checkout_path': os.path.join(self.root_dir, dep.name),
         'expected_url': dep.url,
         'expected_scm': gclient_scm.GetScmName(dep.url),
@@ -1255,6 +1246,9 @@ want to set 'managed': False in .gclient.
     """
     if not self.dependencies:
       raise gclient_utils.Error('No solution specified')
+
+    self._CheckConfig()
+
     revision_overrides = {}
     # It's unnecessary to check for revision overrides for 'recurse'.
     # Save a few seconds by not calling _EnforceRevisions() in that case.
@@ -1329,7 +1323,6 @@ want to set 'managed': False in .gclient.
             gclient_utils.rmtree(e_dir)
       # record the current list of entries for next time
       self._SaveEntries()
-    self._CheckConfig()
     return 0
 
   def PrintRevInfo(self):