[ios] Fix uses of ios::ChromeBrowserState in /ios/chrome/browser/ui/dialogs

The ChromeBrowserState has been moved from the "ios" namespace
to the global namespace by http://crrev.com/c/2014913. Fix the
uses from ios::ChromeBrowserState to ChromeBrowserState.

Also remove includes of chrome_browser_state_forward.h and use
a simple forward declaration instead (since the old name is no
longer necessary).

This CL was uploaded by git cl split.

R=rkgibson@chromium.org

Bug: 1042208
Change-Id: I56ed201d400ffc56de8ff3b65408e4f0eaddd121
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015095Reviewed-by: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735843}

ios/chrome/browser/ui/dialogs/non_modal/non_modal_alert_coordinator.mm

@@ -30,8 +30,7 @@
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
                                      title:(NSString*)title
                                    message:(NSString*)message
-                              browserState:
-                                  (ios::ChromeBrowserState*)browserState {
+                              browserState:(ChromeBrowserState*)browserState {
   DCHECK(browserState);
   self = [super initWithBaseViewController:viewController
                                      title:title