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

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=justincohen@chromium.org

Bug: 1042208
Change-Id: If3b61d1813d21bd61bda77083fa3b4de3492a9a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2017368Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735284}

ios/chrome/browser/ui/toolbar/adaptive_toolbar_coordinator.h

@@ -29,8 +29,7 @@ class WebStateList;
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
     NS_UNAVAILABLE;
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
-                              browserState:
-                                  (ios::ChromeBrowserState*)browserState
+                              browserState:(ChromeBrowserState*)browserState
     NS_UNAVAILABLE;
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
                                    browser:(Browser*)browser NS_UNAVAILABLE;