Move all core files in //components/sessions into core/ subdir

components/sessions/core/session_id.cc

Index: components/sessions/core/session_id.cc
diff --git a/components/sessions/session_id.cc b/components/sessions/core/session_id.cc
similarity index 83%
rename from components/sessions/session_id.cc
rename to components/sessions/core/session_id.cc
index 6999a2a20105fa16cb493c1359d3274d4c09f3a9..1ab9753a83d8341f899b1836c0210bf9ec622b0c 100644
--- a/components/sessions/session_id.cc
+++ b/components/sessions/core/session_id.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "components/sessions/session_id.h"
+#include "components/sessions/core/session_id.h"
 
 static SessionID::id_type next_id = 1;