Adds the contextMessage field to notifications.

ui/message_center/message_center_style.cc

Index: ui/message_center/message_center_style.cc
diff --git a/ui/message_center/message_center_style.cc b/ui/message_center/message_center_style.cc
index 0289a96c7f2fa9fb9346eed3af59edd8748aa7cf..db86d3e0702afd54e5074750d7b311f675d011da 100644
--- a/ui/message_center/message_center_style.cc
+++ b/ui/message_center/message_center_style.cc
@@ -38,12 +38,15 @@ const int kTitleFontSize = 14;
 const int kTitleLineHeight = 20;
 const int kMessageFontSize = 12;
 const int kMessageLineHeight = 18;
+const int kContextMessageFontSize = 12;
+const int kContextMessageLineHeight = 18;
 
 // Colors.
 const SkColor kNotificationBackgroundColor = SkColorSetRGB(255, 255, 255);
 const SkColor kLegacyIconBackgroundColor = SkColorSetRGB(0xf5, 0xf5, 0xf5);
 const SkColor kRegularTextColor = SkColorSetRGB(34, 34, 34);
 const SkColor kDimTextColor = SkColorSetRGB(102, 102, 102);
+const SkColor kContextTextColor = SkColorSetRGB(80, 80, 80);
 const SkColor kFocusBorderColor = SkColorSetRGB(64, 128, 250);
 
 // Limits.