MacViews a11y: Sync VoiceOver cursor with keyboard focus.

content/browser/accessibility/browser_accessibility_cocoa.mm

 // Copyright (c) 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.
 
 #include <execinfo.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #import "content/browser/accessibility/browser_accessibility_cocoa.h"
 
 #include <map>
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_cftyperef.h"
+#import "base/mac/sdk_forward_declarations.h"
 #include "base/strings/string16.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/app/strings/grit/content_strings.h"
 #include "content/browser/accessibility/browser_accessibility_mac.h"
 #include "content/browser/accessibility/browser_accessibility_manager.h"
 #include "content/browser/accessibility/browser_accessibility_manager_mac.h"
 #include "content/browser/accessibility/one_shot_accessibility_tree_search.h"
 #include "content/public/common/content_client.h"
 #include "third_party/skia/include/core/SkColor.h"
@@ skipping 75 matching lines @@
   int32_t node_id;
   int offset;
   ui::AXTextAffinity affinity;
 };
 
 // VoiceOver uses -1 to mean "no limit" for AXResultsLimit.
 const int kAXResultsLimitNoLimit = -1;
 
 extern "C" {
 
-// See http://openradar.appspot.com/9896491. This SPI has been tested on 10.5,
-// 10.6, and 10.7. It allows accessibility clients to observe events posted on
-// this object.
-void NSAccessibilityUnregisterUniqueIdForUIElement(id element);
-
 // The following are private accessibility APIs required for cursor navigation
 // and text selection. VoiceOver started relying on them in Mac OS X 10.11.
 #if !defined(MAC_OS_X_VERSION_10_11) || \
     MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_11
 
 AXTextMarkerRef AXTextMarkerCreate(CFAllocatorRef allocator,
                                    const UInt8* bytes,
                                    CFIndex length);
 
 const UInt8* AXTextMarkerGetBytePtr(AXTextMarkerRef text_marker);
@@ skipping 471 matching lines @@
   dict = nil;
 }
 
 - (instancetype)initWithObject:(BrowserAccessibility*)accessibility {
   if ((self = [super init]))
     browserAccessibility_ = accessibility;
   return self;
 }
 
 - (void)detach {
-  if (browserAccessibility_)
-    NSAccessibilityUnregisterUniqueIdForUIElement(self);
+  if (!browserAccessibility_)
+    return;
+  NSAccessibilityPostNotification(
+      self, NSAccessibilityUIElementDestroyedNotification);
+  NSAccessibilityUnregisterUniqueIdForUIElement(self);
   browserAccessibility_ = nullptr;
 }
 
 - (NSString*)accessKey {
   if (![self instanceActive])
     return nil;
   return NSStringForStringAttribute(
       browserAccessibility_, ui::AX_ATTR_ACCESS_KEY);
 }
 
@@ skipping 2228 matching lines @@
   return ([self hash] == [object hash]);
 }
 
 - (NSUInteger)hash {
   // Potentially called during dealloc.
   if (![self instanceActive])
     return [super hash];
   return browserAccessibility_->GetId();
 }
 
+- (BOOL)accessibilityNotifiesWhenDestroyed {
+  return YES;

[tapted, 2016/09/26 05:19:17]

Comment here why this is done? Reading the comment on NSAccessibility.h suggests
to me that this is the right thing to do - but does it solve a specific problem?
(and it look slike OSX provided accessibilityNotifiesWhenDestroyed in the 10.9
SDK to support a particular use case - now that we use it, is there a
possibility of conflict with the accessibilityShouldUseUniqueId stuff?)

[Patti Lor, 2016/09/28 00:29:14]

Ah - I think this might actually not be needed (at least, not while
accessibilityShouldUseUniqueId is also there). I just double checked this (for
Views) and having either or both accessibilityShouldUseUniqueId and
accessibilityNotifiesWhenDestroyed make VO faster than without, so probably only
one is needed. Inside the WebContents though I don't actually notice any
difference in speed when deleting these, only in the Views parts, which is kind
of strange - have no idea why it affects only Views.

Since the former uses a private thing, I went ahead and deleted that in favour
of accessibilityNotifiesWhenDestroyed (so am kind of guessing/assuming they do
the same thing), but let me know if you want to just keep it as is here and use
accessibilityNotifiesWhenDestroyed in AXPlatformNodeCocoa. I don't think they
actually conflict though. 

(To be clear, not having either will make VO really slow in Views only - it will
take at least a couple of seconds to catch up when keyboard focus is moved.)

+}
+
 - (BOOL)accessibilityShouldUseUniqueId {
   return YES;
 }
 
 @end