Make int64 -> Time conversion explicit....

base/time.h

Index: base/time.h
===================================================================
--- base/time.h	(revision 25840)
+++ base/time.h	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -313,10 +313,10 @@
 
   // Return a new time modified by some delta.
   Time operator+(TimeDelta delta) const {
-    return us_ + delta.delta_;
+    return Time(us_ + delta.delta_);
   }
   Time operator-(TimeDelta delta) const {
-    return us_ - delta.delta_;
+    return Time(us_ - delta.delta_);
   }
 
   // Comparison operators
@@ -350,7 +350,7 @@
   // |is_local = true| or UTC |is_local = false|.
   static Time FromExploded(bool is_local, const Exploded& exploded);
 
-  Time(int64 us) : us_(us) {
+  explicit Time(int64 us) : us_(us) {
   }
 
   // The representation of Jan 1, 1970 UTC in microseconds since the