[ios] Correctly determine last seen WKNavigation object.

ios/web/web_state/ui/crw_wk_navigation_states.mm

+// 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.
+
+#import "ios/web/web_state/ui/crw_wk_navigation_states.h"
+
+#include "base/logging.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+// Holds a pair of state and creation order index.
+@interface CRWWKNavigationsStateRecord : NSObject
+// Navigation state.
+@property(nonatomic, assign) web::WKNavigationState state;
+// Numerical index representing creation order (smaller index denotes earlier
+// navigations).
+@property(nonatomic, assign, readonly) NSUInteger index;
+
+- (instancetype)init NS_UNAVAILABLE;
+
+// Initializes record with state and index values.
+- (instancetype)initWithState:(web::WKNavigationState)state
+                        index:(NSUInteger)index NS_DESIGNATED_INITIALIZER;
+
+@end
+
+@implementation CRWWKNavigationsStateRecord
+@synthesize state = _state;
+@synthesize index = _index;
+
+- (NSString*)description {
+  return [NSString stringWithFormat:@"state: %d, index: %ld", _state, _index];
+}
+
+- (instancetype)initWithState:(web::WKNavigationState)state
+                        index:(NSUInteger)index {
+  if ((self = [super init])) {
+    _state = state;
+    _index = index;
+  }
+  return self;
+}
+
+@end
+
+@interface CRWWKNavigationStates () {
+  NSMapTable* _records;
+  NSUInteger _lastStateIndex;
+}
+@end
+
+@implementation CRWWKNavigationStates
+
+- (instancetype)init {
+  if ((self = [super init])) {
+    _records = [NSMapTable weakToStrongObjectsMapTable];
+  }
+  return self;
+}
+
+- (NSString*)description {
+  return [NSString stringWithFormat:@"records: %@, lastAddedNavigation: %@",
+                                    _records, self.lastAddedNavigation];
+}
+
+- (void)addNavigation:(WKNavigation*)navigation
+             forState:(web::WKNavigationState)state {
+  if (!navigation) {
+    // WKWebView may call WKNavigationDelegate callbacks with nil
+    // |WKNavigation|. TODO(crbug.com/677354): Remove this once WKWebView bug
+    // is fixed.
+    return;
+  }
+
+  CRWWKNavigationsStateRecord* record = [_records objectForKey:navigation];
+  if (!record) {
+    DCHECK(state == web::WK_NAVIGATION_STATE_REQUESTED ||
+           state == web::WK_NAVIGATION_STATE_STARTED ||
+           state == web::WK_NAVIGATION_STATE_COMMITTED);
+    record =
+        [[CRWWKNavigationsStateRecord alloc] initWithState:state
+                                                     index:++_lastStateIndex];
+  } else {
+    DCHECK_GT(state, record.state);
+    record.state = state;
+  }
+  [_records setObject:record forKey:navigation];
+}
+
+- (WKNavigation*)lastAddedNavigation {
+  WKNavigation* result = nil;
+  NSUInteger lastAddedIndex = 0;  // record indices srart with 1.
+  for (WKNavigation* navigation in _records) {
+    CRWWKNavigationsStateRecord* record = [_records objectForKey:navigation];
+    if (lastAddedIndex < record.index) {
+      result = navigation;
+      lastAddedIndex = record.index;
+    }
+  }
+  return result;
+}
+
+- (web::WKNavigationState)stateForNavigation:(WKNavigation*)navigation {
+  CRWWKNavigationsStateRecord* record = [_records objectForKey:navigation];
+  return record.state;
+}
+
+@end