[ios] Unified CRWSessionController navigation logic.

ios/web/navigation/crw_session_controller.mm

 // Copyright 2012 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/navigation/crw_session_controller.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 618 matching lines @@
 
 - (void)goBack {
   [self goDelta:-1];
 }
 
 - (void)goForward {
   [self goDelta:1];
 }
 
 - (void)goDelta:(int)delta {
-  if (delta == 0 || ![self canGoDelta:delta])
-    return;
-
-  NSInteger oldNavigationIndex = self.currentNavigationIndex;
-  NSInteger newNavigationIndex = [self indexOfEntryForDelta:delta];
-
-  if (delta < 0) {
-    [self discardNonCommittedEntries];
-    for (int i = delta; i < 0; i++) {
-      base::RecordAction(UserMetricsAction("Back"));
-    }
-  } else if (delta > 0) {
-    [self discardTransientEntry];
-    for (int i = 0; i < delta; i++) {
-      base::RecordAction(UserMetricsAction("Forward"));
-    }
+  if (delta != 0 && [self canGoDelta:delta]) {
+    NSInteger newNavigationIndex = [self indexOfEntryForDelta:delta];
+    [self goToEntry:_entries[newNavigationIndex]];
   }
-
-  _currentNavigationIndex = newNavigationIndex;
-  _previousNavigationIndex = oldNavigationIndex;
 }
 
 - (void)goToEntry:(CRWSessionEntry*)entry {
   DCHECK(entry);
+  if (![_entries containsObject:entry])
+    return;
 
-  [self discardTransientEntry];
+  NSInteger newNavigationIndex = [_entries indexOfObject:entry];
+  NSInteger delta = newNavigationIndex - _currentNavigationIndex;
+  if (delta < 0) {
+    for (int i = delta; i < 0; i++) {
+      base::RecordAction(UserMetricsAction("Back"));
+    }
+    [self discardNonCommittedEntries];
+  } else if (0 < delta) {
+    for (int i = 0; i < delta; i++) {
+      base::RecordAction(UserMetricsAction("Forward"));
+    }
+    [self discardTransientEntry];
+  } else {
+    // delta is 0, no need to change current navigation index.
+    return;
+  }
 
-  // Check that |entries_| still contains |entry|. |entry| could have been
-  // removed by -clearForwardEntries.
-  if ([_entries containsObject:entry]) {
-    _previousNavigationIndex = self.currentNavigationIndex;
-    self.currentNavigationIndex = [_entries indexOfObject:entry];
-  }
+  _previousNavigationIndex = _currentNavigationIndex;
+  _currentNavigationIndex = newNavigationIndex;
 }
 
 - (void)removeEntryAtIndex:(NSInteger)index {
   DCHECK(index < static_cast<NSInteger>([_entries count]));
   DCHECK(index != _currentNavigationIndex);
   DCHECK(index >= 0);
 
   [self discardNonCommittedEntries];
 
   [_entries removeObjectAtIndex:index];
@@ skipping 199 matching lines @@
   item->set_is_renderer_initiated(rendererInitiated);
   return [[CRWSessionEntry alloc] initWithNavigationItem:std::move(item)];
 }
 
 - (BOOL)isRedirectTransitionForEntryAtIndex:(NSInteger)index {
   ui::PageTransition transition = [self transitionForIndex:index];
   return (transition & ui::PAGE_TRANSITION_IS_REDIRECT_MASK) ? YES : NO;
 }
 
 @end