Avoid sending IDC_BACK/FORWARD when back/forward is not possible

ios/chrome/browser/ui/key_commands_provider.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/chrome/browser/ui/key_commands_provider.h"
 
 #import "base/ios/weak_nsobject.h"
 #include "base/logging.h"
 #include "components/strings/grit/components_strings.h"
 #import "ios/chrome/browser/ui/commands/generic_chrome_command.h"
@@ skipping 24 matching lines @@
 
   const BOOL useRTLLayout = UseRTLLayout();
   const NSInteger browseLeft = useRTLLayout ? IDC_FORWARD : IDC_BACK;
   const NSInteger browseRight = useRTLLayout ? IDC_BACK : IDC_FORWARD;
   const int browseLeftDescriptionID = useRTLLayout
                                           ? IDS_IOS_KEYBOARD_HISTORY_FORWARD
                                           : IDS_IOS_KEYBOARD_HISTORY_BACK;
   const int browseRightDescriptionID = useRTLLayout
                                            ? IDS_IOS_KEYBOARD_HISTORY_BACK
                                            : IDS_IOS_KEYBOARD_HISTORY_FORWARD;
+  BOOL (^canBrowseLeft)() = [[^() {
+    return useRTLLayout ? [weakConsumer canGoForward]
+                        : [weakConsumer canGoBack];
+  } copy] autorelease];
+  BOOL (^canBrowseRight)() = [[^() {
+    return useRTLLayout ? [weakConsumer canGoBack]
+                        : [weakConsumer canGoForward];
+  } copy] autorelease];
 
   // Initialize the array of commands with an estimated capacity.
   NSMutableArray* keyCommands = [NSMutableArray arrayWithCapacity:32];
 
   // List the commands that always appear in the HUD. They appear in the HUD
   // since they have titles.
   [keyCommands addObjectsFromArray:@[
     [UIKeyCommand cr_keyCommandWithInput:@"t"
                            modifierFlags:UIKeyModifierCommand
                                    title:l10n_util::GetNSStringWithFixup(
@@ skipping 80 matching lines @@
 
     // Since cmd+left and cmd+right are valid system shortcuts when editing
     // text, don't register those if text is being edited.
     if (!editingText) {
       [keyCommands addObjectsFromArray:@[
         [UIKeyCommand cr_keyCommandWithInput:UIKeyInputLeftArrow
                                modifierFlags:UIKeyModifierCommand
                                        title:l10n_util::GetNSStringWithFixup(
                                                  browseLeftDescriptionID)
                                       action:^{
-                                        execute(browseLeft);
+                                        if (canBrowseLeft()) {
+                                          execute(browseLeft);
+                                        }
                                       }],
         [UIKeyCommand cr_keyCommandWithInput:UIKeyInputRightArrow
                                modifierFlags:UIKeyModifierCommand
                                        title:l10n_util::GetNSStringWithFixup(
                                                  browseRightDescriptionID)
                                       action:^{
-                                        execute(browseRight);
+                                        if (canBrowseRight()) {
+                                          execute(browseRight);
+                                        }
                                       }],
       ]];
     }
 
     NSString* voiceSearchTitle = l10n_util::GetNSStringWithFixup(
         IDS_IOS_VOICE_SEARCH_KEYBOARD_DISCOVERY_TITLE);
     [keyCommands addObjectsFromArray:@[
       [UIKeyCommand cr_keyCommandWithInput:@"y"
                              modifierFlags:UIKeyModifierCommand
                                      title:l10n_util::GetNSStringWithFixup(
@@ skipping 38 matching lines @@
   ]];
 
   // List the commands that don't appear in the HUD and only appear when there
   // is at least a tab.
   if (hasTabs) {
     [keyCommands addObjectsFromArray:@[
       [UIKeyCommand cr_keyCommandWithInput:@"["
                              modifierFlags:UIKeyModifierCommand
                                      title:nil
                                     action:^{
-                                      execute(browseLeft);
+                                      if (canBrowseLeft()) {
+                                        execute(browseLeft);
+                                      }
                                     }],
       [UIKeyCommand cr_keyCommandWithInput:@"]"
                              modifierFlags:UIKeyModifierCommand
                                      title:nil
                                     action:^{
-                                      execute(browseRight);
+                                      if (canBrowseRight()) {
+                                        execute(browseRight);
+                                      }
                                     }],
       [UIKeyCommand cr_keyCommandWithInput:@"."
                              modifierFlags:UIKeyModifierCommand
                                      title:nil
                                     action:^{
                                       execute(IDC_STOP);
                                     }],
       [UIKeyCommand cr_keyCommandWithInput:@"?"
                              modifierFlags:UIKeyModifierCommand
                                      title:nil
@@ skipping 68 matching lines @@
                           action:^{
                             [weakConsumer focusNextTab];
                           }],
     ]];
   }
 
   return keyCommands;
 }
 
 @end