Change eventTime field to standard chrome.* API format.

chrome/common/extensions/api/experimental_notification.idl

Index: chrome/common/extensions/api/experimental_notification.idl
diff --git a/chrome/common/extensions/api/experimental_notification.idl b/chrome/common/extensions/api/experimental_notification.idl
index 582c9b63153f69c753f10c17994e6f2836571a0d..a59c630fb627f5a249f47578fe33ce781387dc62 100644
--- a/chrome/common/extensions/api/experimental_notification.idl
+++ b/chrome/common/extensions/api/experimental_notification.idl
@@ -48,11 +48,9 @@
     // is default.
     long? priority;
 
-    // A timestamp associated with the notification, in W3C ISO 8601 format
-    // (http://www.w3.org/TR/NOTE-datetime) or ECMAScript date time string
-    // format (http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.15)
-    // as generated by date.toISOString(), for example "1994-11-15T12:45:26Z."
-    DOMString? eventTime;
+    // A timestamp associated with the notification, in milliseconds past the
+    // epoch (e.g. <code>Date.now() + n</code>).
+    double? eventTime;
 
     // Smaller version of the icon.
     DOMString? secondIconUrl;