[ios] Correctly determine last seen WKNavigation object.

ios/web/web_state/ui/crw_wk_navigation_states.h

+// Copyright 2016 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.
+
+#ifndef IOS_WEB_WEB_STATE_UI_CRW_WK_NAVIGATION_STATES_H_
+#define IOS_WEB_WEB_STATE_UI_CRW_WK_NAVIGATION_STATES_H_
+
+#import <Foundation/Foundation.h>
+#import <WebKit/WebKit.h>
+
+namespace web {
+
+// State of in-flight WKNavigation objects.
+enum class WKNavigationState : int {
+  // WKNavigation returned from |loadRequest:|, |goToBackForwardListItem:|,
+  // |loadFileURL:allowingReadAccessToURL:|, |loadHTMLString:baseURL:|,
+  // |loadData:MIMEType:characterEncodingName:baseURL:|, |goBack|, |goForward|,
+  // |reload| or |reloadFromOrigin|.
+  REQUESTED = 1,
+  // WKNavigation passed to |webView:didStartProvisionalNavigation:|.
+  STARTED,
+  // WKNavigation passed to
+  // |webView:didReceiveServerRedirectForProvisionalNavigation:|.
+  REDIRECTED,
+  // WKNavigation passed to |webView:didFailProvisionalNavigation:|.
+  PROVISIONALY_FAILED,
+  // WKNavigation passed to |webView:didCommitNavigation:|.
+  COMMITTED,
+  // WKNavigation passed to |webView:didFinishNavigation:|.
+  FINISHED,
+  // WKNavigation passed to |webView:didFailNavigation:withError:|.
+  FAILED,
+};
+
+}  // namespace web
+
+// Stores states for WKNavigation objects. Allows lookign up for last added
+// navigation object.
+@interface CRWWKNavigationStates : NSObject
+
+// Adds a new navigation if it was not added yet. If navigation was already
+// added then updates state for existing navigation. Updating state does not
+// affect the result of |lastAddedNavigation| method. New added navigations
+// should have either WKNavigationState::REQUESTED or WKNavigationState::STARTED

[kkhorimoto, 2017/01/04 00:13:57]

Just noticed now, but this should be updated to also include
WKNavigationState::COMMITTED, since that is also allowed in your DCHECK.

[Eugene But (OOO till 7-30), 2017/01/04 00:20:11]

Done.

+// state. Passed |navigation| will be help as weak reference and will not be
+// retained. No-op if |navigation| is null.
+- (void)setState:(web::WKNavigationState)state
+    forNavigation:(WKNavigation*)navigation;
+
+// WKNavigation which was added the most recently via |setState:forNavigation:|.
+// Updating navigation state via |setState:forNavigation:| does not change the
+// last added navigation. Returns nil if there are no stored navigations.
+- (WKNavigation*)lastAddedNavigation;
+
+// Returns state of the given navigation or 0 if navigation does not exist.

[kkhorimoto, 2017/01/04 00:13:57]

What is returned here using enum classes?  Not sure what default value would be
returned; we might want to add a NONE = 0 to be used for this scenario.

[Eugene But (OOO till 7-30), 2017/01/04 00:20:11]

0 of int type. Added |NONE = 0|.

+- (web::WKNavigationState)stateForNavigation:(WKNavigation*)navigation;
+
+@end
+
+#endif  // IOS_WEB_WEB_STATE_UI_CRW_WK_NAVIGATION_STATES_H_