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/cellular_capability_gsm_unittest.cc b/cellular_capability_gsm_unittest.cc
index df3b06a..18593bb 100644
--- a/cellular_capability_gsm_unittest.cc
+++ b/cellular_capability_gsm_unittest.cc
@@ -55,7 +55,8 @@
 class CellularCapabilityGSMTest : public testing::Test {
  public:
   CellularCapabilityGSMTest()
-      : create_card_proxy_from_factory_(false),
+      : metrics_(&dispatcher_),
+        create_card_proxy_from_factory_(false),
         proxy_(new MockModemProxy()),
         simple_proxy_(new MockModemSimpleProxy()),
         card_proxy_(new MockModemGSMCardProxy()),