Fix progress bar indicator for accessibility.

The progress bar was not being read properly by screen readers for the
Mac (VoiceOver).  This gives the screen reader enough information to
do its job.

BUG=370512

Review URL: https://codereview.chromium.org/333643007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277880 0039d316-1c4b-4281-b951-d872f2087c98

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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