shill: Add Network.Shill.Cellular.TimeToEnable metrics.

This metric tracks the amount of time it takes the modem manager to
enable the modem.

BUG=chromium-os:38086
TEST=Unit tests, check chrome://histograms for new metrics

Change-Id: Ie12e8cee20586f4ebf0070721c6327c13c175474
Reviewed-on: https://gerrit.chromium.org/gerrit/41878
Reviewed-by: Arman Uguray <armansito@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Thieu Le <thieule@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
diff --git a/cellular_capability_gsm.cc b/cellular_capability_gsm.cc
index e76438c..a9ca732 100644
--- a/cellular_capability_gsm.cc
+++ b/cellular_capability_gsm.cc
@@ -51,8 +51,9 @@
 
 
 CellularCapabilityGSM::CellularCapabilityGSM(Cellular *cellular,
-                                             ProxyFactory *proxy_factory)
-    : CellularCapabilityClassic(cellular, proxy_factory),
+                                             ProxyFactory *proxy_factory,
+                                             Metrics *metrics)
+    : CellularCapabilityClassic(cellular, proxy_factory, metrics),
       weak_ptr_factory_(this),
       registration_state_(MM_MODEM_GSM_NETWORK_REG_STATUS_UNKNOWN),
       access_technology_(MM_MODEM_GSM_ACCESS_TECH_UNKNOWN),