Turn off accessibility access to notification images.

ui/message_center/cocoa/notification_controller.mm

Index: ui/message_center/cocoa/notification_controller.mm
diff --git a/ui/message_center/cocoa/notification_controller.mm b/ui/message_center/cocoa/notification_controller.mm
index d2c8bf387c78655c690a77bcf9826822d38d9dc8..cd56b84ca249e8a34e9fabeda274a86b691e270e 100644
--- a/ui/message_center/cocoa/notification_controller.mm
+++ b/ui/message_center/cocoa/notification_controller.mm
@@ -203,10 +203,24 @@
 @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 {

[Robert Sesek, 2014/06/11 21:37:04]

nit: space after - but not after )

[Robert Sesek, 2014/06/11 21:37:04]

nit: no space after ) in arguments

[Pete Williamson, 2014/06/11 22:12:54]

Done.

[Pete Williamson, 2014/06/11 22:12:54]

Done.

+  // If we get a request for NSAccessibilityChildrenAttribute, return an empty
+  // array to pretend we have no children.
+  if ([attribute isEqualToString:NSAccessibilityChildrenAttribute])
+    return [[[NSMutableArray alloc] init] autorelease];

[Robert Sesek, 2014/06/11 21:37:04]

nit: use [NSMutableArray array], or if it does not have to be mutable, just @[]

[Pete Williamson, 2014/06/11 22:12:54]

Done.

+  else
+    return [super accessibilityAttributeValue:attribute];
+}
 @end
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -297,8 +311,7 @@
   [rootView addSubview:closeButton_];
 
   // Create the small image.
-  [self configureSmallImageInFrame:rootFrame];
-  [[self view] addSubview:smallImage_];
+  [rootView addSubview:[self createSmallImageInFrame:rootFrame]];
 
   NSRect contentFrame = [self currentContentRect];
 
@@ -732,7 +745,7 @@
                        forAttribute:NSAccessibilityTitleAttribute];
 }
 
-- (void)configureSmallImageInFrame:(NSRect)rootFrame {
+- (NSView*)createSmallImageInFrame:(NSRect)rootFrame {
   int smallImageXOffset =
       message_center::kSmallImagePadding + message_center::kSmallImageSize;
   NSRect smallImageFrame =
@@ -740,9 +753,19 @@
                  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:smallImageFrame]);
+  [self configureCustomBox:imageBox];
+  [imageBox setAutoresizingMask:NSViewMinYMargin];
   smallImage_.reset([[NSImageView alloc] initWithFrame:smallImageFrame]);

[Robert Sesek, 2014/06/11 21:37:04]

Is this frame still correct? Since it's no longer a subview of |rootView|, its
positioning may be off.

[Pete Williamson, 2014/06/11 22:12:54]

The imageBox is supposed to be the same size and position as the smallImage_. 
This implementation is copied from the createIconView method, which does the
same thing.  As long as both boxes are the same size, I would expect this to
still be valid (I'm by no means an expert in this code, though, so I could have
missed something.) 

[Robert Sesek, 2014/06/12 13:31:10]

Unless I'm misreading the code, it's not quite the same. (Have you tested this
visually, does it look right?) The frame is the position and size of a view in
relation to its superview. In -createIconView, the view placed inside the box
has an origin of (0,0), not the origin relative to the rootView, because it's
not inside the rootView. Here the image is being placed inside the box at an
origin relative to rootView, even though rootView is not its parent: the box is.

https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CocoaV...

[Pete Williamson, 2014/06/12 17:29:04]

Ah, I see.  The code I cut and pasted worked since it was at the origin.  Fixed
to use a separate box
starting at 0,0 for the inner image.  I had not tested the image positioning
before (most of our test messages leave the field blank), but I have now with
the change, and it is working properly.

   [smallImage_ setImageScaling:NSImageScaleProportionallyUpOrDown];
-  [smallImage_ setAutoresizingMask:NSViewMinYMargin];
+  [imageBox setContentView:smallImage_];
+
+  return imageBox.autorelease();
 }
 
 - (void)configureTitleInFrame:(NSRect)contentFrame {