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..74c62122ce453201089e346aa6394de32f6d5a5a 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -349,10 +349,46 @@ 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]) {
+    return NO;
+  }
+
+  if ([attributeName isEqualToString:NSAccessibilityValueAttribute])
+    return node_->GetDelegate()->CanSetStringValue();
+  // TODO(patricialor): Implement and merge with conditional for value above.
+  if ([attributeName isEqualToString:NSAccessibilitySelectedTextAttribute])
+    return NO;
+
+  if ([attributeName isEqualToString:NSAccessibilityFocusedAttribute]) {
+    if (ui::AXViewState::IsFlagSet(node_->GetData().state,
+                                   ui::AX_STATE_FOCUSABLE))
+      return NO;
+  }
+
+  // TODO(patricialor): Add callbacks for updating the above attributes except
+  // NSAccessibilityValueAttribute and return YES.
   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
+  // specified in accessibilityIsAttributeSettable.
+}
+
 - (id)accessibilityAttributeValue:(NSString*)attribute {
   SEL selector = NSSelectorFromString(attribute);
   if ([self respondsToSelector:selector])