shill: cellular: Add Network.Shill.Cellular.DropsPerHour.

BUG=chromium-os:38557
TEST=Unit tests, manually lose LTE signal and check chrome://histograms

Change-Id: I82aa1edabd21c5dfde4834cd36a34a12b629ba8f
Reviewed-on: https://gerrit.chromium.org/gerrit/42813
Reviewed-by: Arman Uguray <armansito@chromium.org>
Commit-Queue: Thieu Le <thieule@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
diff --git a/modem_manager_unittest.cc b/modem_manager_unittest.cc
index 4266737..2014b13 100644
--- a/modem_manager_unittest.cc
+++ b/modem_manager_unittest.cc
@@ -61,7 +61,8 @@
 class ModemManagerTest : public Test {
  public:
   ModemManagerTest()
-      : manager_(&control_interface_, &dispatcher_, &metrics_, &glib_) {
+      : metrics_(&dispatcher_),
+        manager_(&control_interface_, &dispatcher_, &metrics_, &glib_) {
   }
 
   virtual void SetUp() {