Turn off accessibility access to notification images.

Since we don't have alt text yet, accessibility screen readers have
nothing useful to say in screen readers.  Until alt text is available,
disable the images from appearing in the screen reader.

This is done by removing the accessibility child object from a parent.
In this case, we introduce a new fake parent object for the small icon,
and make the existing parent ignore the image for the large icon and
the large image of an image notification.

BUG=381363

Review URL: https://codereview.chromium.org/325203003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277957 0039d316-1c4b-4281-b951-d872f2087c98

ui/message_center/cocoa/notification_controller.mm

@@ -218,10 +218,24 @@
 @interface AccessibilityIgnoredBox : NSBox
 @end
 
+// Ignore this element, but expose its children to accessibility.
 @implementation AccessibilityIgnoredBox
 - (BOOL)accessibilityIsIgnored {
   return YES;
 }
+
+// Pretend this element has no children.
+// TODO(petewil): Until we have alt text available, we will hide the children of
+//  the box also.  Remove this override once alt text is set (by using
+// NSAccessibilityDescriptionAttribute).
+- (id)accessibilityAttributeValue:(NSString*)attribute {
+  // If we get a request for NSAccessibilityChildrenAttribute, return an empty
+  // array to pretend we have no children.
+  if ([attribute isEqualToString:NSAccessibilityChildrenAttribute])
+    return @[];
+  else
+    return [super accessibilityAttributeValue:attribute];
+}
 @end
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -312,8 +326,7 @@
   [rootView addSubview:closeButton_];
 
   // Create the small image.
-  [self configureSmallImageInFrame:rootFrame];
-  [[self view] addSubview:smallImage_];
+  [rootView addSubview:[self createSmallImageInFrame:rootFrame]];
 
   NSRect contentFrame = [self currentContentRect];
 
@@ -747,17 +760,33 @@
                        forAttribute:NSAccessibilityTitleAttribute];
 }
 
-- (void)configureSmallImageInFrame:(NSRect)rootFrame {
+- (NSView*)createSmallImageInFrame:(NSRect)rootFrame {
   int smallImageXOffset =
       message_center::kSmallImagePadding + message_center::kSmallImageSize;
-  NSRect smallImageFrame =
+  NSRect boxFrame =
       NSMakeRect(NSMaxX(rootFrame) - smallImageXOffset,
                  NSMinY(rootFrame) + message_center::kSmallImagePadding,
                  message_center::kSmallImageSize,
                  message_center::kSmallImageSize);
+
+  // Put the smallImage inside another box which can hide it from accessibility
+  // until we have some alt text to go with it.  Once we have alt text, remove
+  // the box, and set NSAccessibilityDescriptionAttribute with it.
+  base::scoped_nsobject<NSBox> imageBox(
+      [[AccessibilityIgnoredBox alloc] initWithFrame:boxFrame]);
+  [self configureCustomBox:imageBox];
+  [imageBox setAutoresizingMask:NSViewMinYMargin];
+
+  NSRect smallImageFrame =
+      NSMakeRect(0,0,
+                 message_center::kSmallImageSize,
+                 message_center::kSmallImageSize);
+
   smallImage_.reset([[NSImageView alloc] initWithFrame:smallImageFrame]);
   [smallImage_ setImageScaling:NSImageScaleProportionallyUpOrDown];
-  [smallImage_ setAutoresizingMask:NSViewMinYMargin];
+  [imageBox setContentView:smallImage_];
+
+  return imageBox.autorelease();
 }
 
 - (void)configureTitleInFrame:(NSRect)contentFrame {