[Mac][MC] Adjust the size of the status item view based on the unread count.

ui/message_center/cocoa/status_item_view_unittest.mm

Index: ui/message_center/cocoa/status_item_view_unittest.mm
diff --git a/ui/message_center/cocoa/status_item_view_unittest.mm b/ui/message_center/cocoa/status_item_view_unittest.mm
index 075e23a5d9a7829e62bb0f3d48da446314b02612..6bffcf439c9cc465ab96a62ce9369d7a4dcbeb02 100644
--- a/ui/message_center/cocoa/status_item_view_unittest.mm
+++ b/ui/message_center/cocoa/status_item_view_unittest.mm
@@ -43,14 +43,32 @@ TEST_F(StatusItemViewTest, Callback) {
 }
 
 TEST_F(StatusItemViewTest, UnreadCount) {
+  CGFloat initial_width = NSWidth([view_ frame]);
+
+  CGFloat width = initial_width;
   [view_ setUnreadCount:2];
   [view_ display];
+  EXPECT_GT(NSWidth([view_ frame]), width);
+  width = NSWidth([view_ frame]);
+
   [view_ setUnreadCount:10];
   [view_ display];
+  EXPECT_GT(NSWidth([view_ frame]), width);
+  width = NSWidth([view_ frame]);
+
+  CGFloat max_width = width;
+
   [view_ setUnreadCount:0];
   [view_ display];
+  EXPECT_LT(NSWidth([view_ frame]), width);
+  width = NSWidth([view_ frame]);
+  EXPECT_CGFLOAT_EQ(width, initial_width);
+
   [view_ setUnreadCount:1000];
   [view_ display];
+  EXPECT_GT(NSWidth([view_ frame]), width);
+  width = NSWidth([view_ frame]);
+  EXPECT_CGFLOAT_EQ(width, max_width);
 }
 
 TEST_F(StatusItemViewTest, Highlight) {