Use FakeServer-based invalidations for Sync tests

sync/test/fake_server/fake_server_http_post_provider.h

Index: sync/test/fake_server/fake_server_http_post_provider.h
diff --git a/sync/test/fake_server/fake_server_http_post_provider.h b/sync/test/fake_server/fake_server_http_post_provider.h
index 63f1eda2b277720569a1018ddf54178cfcd2ce74..5c0223006fe7fb5c7ee09054724b6a9ad5adda98 100644
--- a/sync/test/fake_server/fake_server_http_post_provider.h
+++ b/sync/test/fake_server/fake_server_http_post_provider.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/memory/ref_counted.h"
+#include "base/synchronization/waitable_event.h"
 #include "sync/internal_api/public/http_post_provider_factory.h"
 #include "sync/internal_api/public/http_post_provider_interface.h"
 
@@ -39,6 +40,8 @@ class FakeServerHttpPostProvider
   virtual ~FakeServerHttpPostProvider();
 
  private:
+  void OnPostComplete();
+
   FakeServer* const fake_server_;
   std::string response_;
   std::string request_url_;
@@ -46,6 +49,7 @@ class FakeServerHttpPostProvider
   std::string request_content_;
   std::string request_content_type_;
   std::string extra_request_headers_;
+  base::WaitableEvent post_complete_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeServerHttpPostProvider);
 };