Reland r105404 with compile warning fixed.

chrome/browser/sync/api/syncable_service.h

Index: chrome/browser/sync/api/syncable_service.h
diff --git a/chrome/browser/sync/api/syncable_service.h b/chrome/browser/sync/api/syncable_service.h
index 9d7ae621b7b8cb534a7e2d7b7660a5c99784d81e..a2b021322c80bc699d3fc031f3b63fc142b3e9c6 100644
--- a/chrome/browser/sync/api/syncable_service.h
+++ b/chrome/browser/sync/api/syncable_service.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "chrome/browser/sync/syncable/model_type.h"
 #include "chrome/browser/sync/api/sync_change_processor.h"
 #include "chrome/browser/sync/api/sync_data.h"
@@ -18,7 +19,11 @@ class SyncData;
 
 typedef std::vector<SyncData> SyncDataList;
 
-class SyncableService : public SyncChangeProcessor {
+// TODO(zea): remove SupportsWeakPtr in favor of having all SyncableService
+// implementers provide a way of getting a weak pointer to themselves.
+// See crbug.com/100114.
+class SyncableService : public SyncChangeProcessor,
+                        public base::SupportsWeakPtr<SyncableService> {
  public:
   // Informs the service to begin syncing the specified synced datatype |type|.
   // The service should then merge |initial_sync_data| into it's local data,