MacViews a11y: Allow accessibility clients to set the AXValue on some controls.

ui/accessibility/platform/ax_platform_node_mac.mm

Index: ui/accessibility/platform/ax_platform_node_mac.mm
diff --git a/ui/accessibility/platform/ax_platform_node_mac.mm b/ui/accessibility/platform/ax_platform_node_mac.mm
index 79fa94904ba8d2fbd2fcb4f57b97db3fa7f8ca29..df018cc47e10bf47b349dfecfc37a91cff75cd40 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -349,10 +349,49 @@ void NotifyMacEvent(NSView* target, ui::AXEvent event_type) {
   return axAttributes.autorelease();
 }
 
-- (BOOL)accessibilityIsAttributeSettable:(NSString*)attribute {
+- (BOOL)accessibilityIsAttributeSettable:(NSString*)attributeName {
+  // Allow certain attributes to be written via an accessibility client. A
+  // writable attribute will only appear as such if the accessibility element
+  // has a value set for that attribute.
+  if ([attributeName isEqualToString:NSAccessibilitySelectedAttribute] ||
+      [attributeName
+          isEqualToString:NSAccessibilitySelectedChildrenAttribute] ||
+      [attributeName
+          isEqualToString:NSAccessibilitySelectedTextRangeAttribute] ||
+      [attributeName
+          isEqualToString:NSAccessibilityVisibleCharacterRangeAttribute]) {
+    if (!ui::AXViewState::IsFlagSet(node_->GetData().state,
+                                    ui::AX_STATE_READ_ONLY))
+      // TODO(patricialor): Move READ_ONLY check to callbacks.
+      return YES;

[tapted, 2016/08/12 03:50:52]

There might be some specific semantics of ui::AX_STATE_READ_ONLY, but I would
have thought these 4 could return YES unconditionally. E.g. you can still
highlight text on readonly textfields

[Patti Lor, 2016/08/12 05:16:54]

Thanks, didn't know that! Acking this and the next two comments for future CLs.

+  }
+
+  if ([attributeName isEqualToString:NSAccessibilityValueAttribute] ||
+      [attributeName isEqualToString:NSAccessibilitySelectedTextAttribute]) {
+    if (node_->GetDelegate()->CanSetStringValue())

[tapted, 2016/08/12 03:50:52]

perhaps just `return node_->GetDelegate()->CanSetStringValue();`

[Patti Lor, 2016/08/12 05:16:54]

Acknowledged.

+      return YES;
+  }
+
+  if ([attributeName isEqualToString:NSAccessibilityFocusedAttribute]) {
+    if (ui::AXViewState::IsFlagSet(node_->GetData().state,

[tapted, 2016/08/12 03:50:52]

same here - just return the function result

[Patti Lor, 2016/08/12 05:16:54]

Acknowledged.

+                                   ui::AX_STATE_FOCUSABLE))
+      return YES;
+  }
+
+  // TODO(patricialor): Add callbacks for updating the above attributes except
+  // NSAccessibilityValueAttribute.
   return NO;
 }
 
+- (void)accessibilitySetValue:(id)value forAttribute:(NSString*)attribute {
+  if ([attribute isEqualToString:NSAccessibilityValueAttribute] &&
+      [value isKindOfClass:[NSString class]])
+    node_->GetDelegate()->SetStringValue(base::SysNSStringToUTF16(value));
+
+  // TODO(patricialor): Plumb through all the other writable attributes as

[tapted, 2016/08/12 03:50:52]

It might be wrong to already return `YES` for the ones not plumbed through,
since it would silently fail here in those cases. (e.g. consider returning NO
above and putting TODO(..): Implement and return YES.) It's possible we run into
blocking problems implementing some of them, like 'selected children'

Of course, you'd have to ignore my previous two comments :)

[Patti Lor, 2016/08/12 05:16:54]

Done.

+  // specified in accessibilityIsAttributeSettable.
+}
+
 - (id)accessibilityAttributeValue:(NSString*)attribute {
   SEL selector = NSSelectorFromString(attribute);
   if ([self respondsToSelector:selector])