USS SyncContextProxy / data type activation refactoring

This refactoring prepares the code to introduction of
NonBlockingDataTypeController for USS datatypes. The goal
was to split the very large NonBlockingDataTypeController
change into a couple of smaller to make it easier to review
and verify.

The following changes are included here:
1) Introduced ActivationContext which is a structure that
   contains all arguments needed to activate a USS datatype.
   For now ActivationContext is passed via SyncContext /
   SyncContextProxy, but the goal is to pass it directly
   via BackendDataTypeConfigurer as an argument for
   ActivateNonBlockingDataType.
   ActivationContext is needed as a separate class because
   NonBlockingDataTypeController will have to receive it
   from the type processor's callback and temporarily hold
   on to it.
2) BackendDataTypeConfigurer - two activation methods are
   renamed to be directory specific and two more activation
   methods for non-blocking data types are added.
3) DataTypeController cleanup - OnModelLoaded() virtual
   method shouldn't be on the base class because it applies
   only to some of the subclasses and is never invoked via the
   base class.

BUG=515962

Review URL: https://codereview.chromium.org/1368683003

Cr-Commit-Position: refs/heads/master@{#351110}

1 files changed, 13 insertions, 0 deletions

diff --git a/sync/internal_api/activation_context.cc b/sync/internal_api/activation_context.cc
new file mode 100644
index 0000000..d6d5c58
--- /dev/null
+++ b/sync/internal_api/activation_context.cc
@@ -0,0 +1,13 @@
+// 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.
+
+#include "sync/internal_api/public/activation_context.h"
+
+namespace syncer_v2 {
+
+ActivationContext::ActivationContext() {}
+
+ActivationContext::~ActivationContext() {}
+
+}  // namespace syncer_v2