Fix progress bar indicator for accessibility.

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..204f052835fabf261aba13bdbccc216b60049d5c 100644
--- a/ui/message_center/cocoa/notification_controller.mm
+++ b/ui/message_center/cocoa/notification_controller.mm
@@ -51,6 +51,21 @@
   [gfx::SkColorToCalibratedNSColor(message_center::kProgressBarSliceColor) set];
   [path fill];
 }
+
+- (id)accessibilityAttributeValue:(NSString*)attribute {
+  double progressValue = 0.0;
+  if ([attribute isEqualToString:NSAccessibilityDescriptionAttribute]) {
+    progressValue = [self doubleValue];
+  } else if ([attribute isEqualToString:NSAccessibilityMinValueAttribute]) {
+    progressValue = [self minValue];
+  } else if ([attribute isEqualToString:NSAccessibilityMaxValueAttribute]) {
+    progressValue = [self maxValue];
+  } else {
+    return [super accessibilityAttributeValue:attribute];
+  }
+
+  return [NSString stringWithFormat:@"%lf", progressValue];
+}
 @end
 
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