[ios clean] Creates ToolbarWebState Mediator

ios/clean/chrome/browser/ui/toolbar/toolbar_web_state_mediator.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/clean/chrome/browser/ui/toolbar/toolbar_web_state_mediator.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/strings/sys_string_conversions.h"
+#import "ios/clean/chrome/browser/ui/toolbar/toolbar_web_state_consumer.h"
+#include "ios/web/public/web_state/web_state.h"
+
+@implementation ToolbarWebStateMediator {
+  std::unique_ptr<web::WebStateObserverBridge> _webStateObserver;
+}
+
+@synthesize consumer = _consumer;
+@synthesize webState = _webState;
+
+- (void)dealloc {
+  _webStateObserver.reset();
+  _webState = nullptr;
+}
+
+- (void)setWebState:(web::WebState*)webState {
+  _webState = webState;
+  _webStateObserver =
+      base::MakeUnique<web::WebStateObserverBridge>(self.webState, self);
+}
+
+#pragma mark - CRWWebStateObserver
+
+- (void)webState:(web::WebState*)webState didLoadPageWithSuccess:(BOOL)success {
+  const GURL& pageURL = webState->GetVisibleURL();
+  [self.consumer setCurrentPageText:base::SysUTF8ToNSString(pageURL.spec())];

[edchin, 2017/02/21 07:56:12]

The consumer is a UI object therefore this call needs to be on the main thread.
I wonder if we can be certain that this callback is in the main thread?

[marq (ping after 24h), 2017/02/21 12:04:25]

The CRWWebStateObserver and web::WebStateObserver headers should document that;
at the moment they don't. I'm pretty sure those observer methods are only called
on the main thread, but ask Eugene.

[sczs, 2017/02/21 17:28:28]

Asked Eugene and he told me that they all should be called on the main thread
(unless there's a bug of course). I'll send a quick CL later to update those
headers. 

+}
+
+@end