shill: Adds UMA stat for scan time held-off by EBUSY.

BUG=chromium:245908
TEST=unittest and manual.  For manual test, do the following:

  * reboot machine (to force a scan)
  * go to chrome://histograms
  * search for "Network.Shill.WiFi.ScanTimeInEbusy" -- it should be
    there.

Change-Id: I5ff707198cadc23845a40d5beb9d64359e1b5c81
Reviewed-on: https://gerrit.chromium.org/gerrit/57279
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Queue: Wade Guthrie <wdg@chromium.org>
Reviewed-by: Wade Guthrie <wdg@chromium.org>
Tested-by: Wade Guthrie <wdg@chromium.org>
diff --git a/mock_scan_session.cc b/mock_scan_session.cc
index 2791e5d..d5fb922 100644
--- a/mock_scan_session.cc
+++ b/mock_scan_session.cc
@@ -20,7 +20,8 @@
                                  const FractionList &fractions,
                                  int min_frequencies,
                                  int max_frequencies,
-                                 OnScanFailed on_scan_failed)
+                                 OnScanFailed on_scan_failed,
+                                 Metrics *metrics)
     : ScanSession(netlink_manager,
                   dispatcher,
                   previous_frequencies,
@@ -29,7 +30,8 @@
                   fractions,
                   min_frequencies,
                   max_frequencies,
-                  on_scan_failed) {
+                  on_scan_failed,
+                  metrics) {
   ON_CALL(*this, HasMoreFrequencies()).WillByDefault(testing::Return(true));
 }