ash: Separate out SystemTrayBubble and related classes into a new file.

ash/system/tray/tray_constants.cc

Index: ash/system/tray/tray_constants.cc
diff --git a/ash/system/tray/tray_constants.cc b/ash/system/tray/tray_constants.cc
index de787f9ec9a958248c399bf01f423ce4709b2493..d4427e95cdcb5e02ad0f05fc1e4004b77f70398b 100644
--- a/ash/system/tray/tray_constants.cc
+++ b/ash/system/tray/tray_constants.cc
@@ -8,6 +8,9 @@
 
 namespace ash {
 
+const int kPaddingFromRightEdgeOfScreen = 15;
+const int kPaddingFromBottomOfScreen = 10;
+
 const int kTrayPopupAutoCloseDelayInSeconds = 2;
 const int kTrayPopupAutoCloseDelayForTextInSeconds = 5;
 const int kTrayPopupPaddingHorizontal = 18;