Exports gesture manager to a separate file and adds its unittests.

athena/home/home_card_constants.cc

Index: athena/home/home_card_constants.cc
diff --git a/athena/activity/activity.cc b/athena/home/home_card_constants.cc
similarity index 54%
copy from athena/activity/activity.cc
copy to athena/home/home_card_constants.cc
index 6a33f02cb33be1877bb43b4e20875f909ae38c8c..38596c4650571cb3914fa106144a5629978c2489 100644
--- a/athena/activity/activity.cc
+++ b/athena/home/home_card_constants.cc
@@ -2,14 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "athena/activity/public/activity.h"
-
-#include "athena/activity/public/activity_manager.h"
+#include "athena/home/home_card_constants.h"
 
 namespace athena {
 
-Activity::~Activity() {
-  ActivityManager::Get()->RemoveActivity(this);
-}
+const int kHomeCardHeight = 100;
+const int kHomeCardMinimizedHeight = 6;
 
 }  // namespace athena