[Sync] Creating sync_sessions component, moving revisit logic.

components/sync_sessions.gypi

Index: components/sync_sessions.gypi
diff --git a/components/sync_sessions.gypi b/components/sync_sessions.gypi
new file mode 100644
index 0000000000000000000000000000000000000000..78a1f270391e63d1cc3a77490d8e624e4d4bea49
--- /dev/null
+++ b/components/sync_sessions.gypi
@@ -0,0 +1,43 @@
+# Copyright 2015 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.
+
+{
+  'targets': [
+    {
+      # GN version: //components/sync_sessions
+      'target_name': 'sync_sessions',
+      'type': 'static_library',
+      'include_dirs': [
+        '..',
+      ],
+      'dependencies': [
+        '../base/base.gyp:base',
+        '../sync/sync.gyp:sync',
+        'sync_driver',
+      ],
+      'sources': [
+        # Note: sources list duplicated in GN build.
+        'sync_sessions/revisit/current_tab_matcher.cc',
+        'sync_sessions/revisit/current_tab_matcher.h',
+        'sync_sessions/revisit/offset_tab_matcher.cc',
+        'sync_sessions/revisit/offset_tab_matcher.h',
+        'sync_sessions/revisit/page_equality.h',
+        'sync_sessions/revisit/page_visit_observer.h',
+        'sync_sessions/revisit/sessions_page_revisit_observer.cc',
+        'sync_sessions/revisit/sessions_page_revisit_observer.h',
+      ],
+      'conditions': [
+        ['OS!="ios"', {
+          'dependencies': [
+            'sessions_content',
+          ],
+        }, {  # OS==ios
+          'dependencies': [
+            'sessions_ios',
+          ],
+        }],
+      ],
+    },
+  ],
+}