[SYNC] Sessions datatype refactor. Most things related to sessions under-the-...

chrome/browser/sync/protocol/session_specifics.proto

Index: chrome/browser/sync/protocol/session_specifics.proto
===================================================================
--- chrome/browser/sync/protocol/session_specifics.proto	(revision 68844)
+++ chrome/browser/sync/protocol/session_specifics.proto	(working copy)
@@ -13,14 +13,20 @@
 
 import "sync.proto";
 
-// Properties of session sync objects.
 message SessionSpecifics {
-  // Unique id for the session.
+  // Unique id for the client.
   optional string session_tag = 1;
+  optional SessionHeader header = 2;
+  optional SessionTab tab = 3;  
+}
+// Properties of session sync objects.
+message SessionHeader {
   // Each session is composed of windows.
-  repeated SessionWindow session_window = 2;
+  repeated SessionWindow window = 2;
 }
 message SessionWindow {
+// Unique (to the owner) id for this window.
+  optional int32 window_id = 1;
   // Index of the selected tab in tabs; -1 if no tab is selected.
   optional int32 selected_tab_index = 2 [default = -1];
   // Type of the browser. Currently we only store browsers of type
@@ -30,22 +36,26 @@
     TYPE_POPUP = 2;
   }
   optional BrowserType browser_type = 3 [default = TYPE_NORMAL];
-  // The tabs that compose a window.
-  repeated SessionTab session_tab= 4;
+  // The tabs that compose a window (correspond to tab id's).
+  repeated int32 tab = 4;
 }
 message SessionTab {
+  // Unique (to the owner) id for this tab.
+  optional int32 tab_id = 1;
+  // The unique id for the window this tab belongs to.
+  optional int32 window_id = 2;
   // Visual index of the tab within its window. There may be gaps in these
   // values.
-  optional int32 tab_visual_index = 2 [default = -1];
+  optional int32 tab_visual_index = 3 [default = -1];
   // Identifies the index of the current navigation in navigations. For
   // example, if this is 2 it means the current navigation is navigations[2].
-  optional int32 current_navigation_index = 3 [default = -1];
+  optional int32 current_navigation_index = 4 [default = -1];
   // True if the tab is pinned.
-  optional bool pinned = 4 [default = false];
+  optional bool pinned = 5 [default = false];
   // If non-empty, this tab is an app tab and this is the id of the extension.
-  optional string extension_app_id = 5;
+  optional string extension_app_id = 6;
   // Tabs are navigated, and the navigation data is here.
-  repeated TabNavigation navigation = 6;
+  repeated TabNavigation navigation = 7;
 }
 message TabNavigation {
   // The index in the NavigationController. If this is -1, it means this