update_engine: Send UMA stats about kernel key versions

Adding the following UMA stats:
- UpdateEngine.KernelKey.MinVersion: Minimum kernel key version
  already set in the TPM.
- UpdateEngine.KernelKey.MaxRollforwardVersion: Maximum kernel key
  rollforward version set by update_engine.
- UpdateEngine.KernelKey.MaxRollforwardSetSuccess: Whether setting
  the maximum kernely key rollforward version succeeded.

Chromium CL of the new histograms: crrev.com/c/1078750

BUG=chromium:843622
TEST='cros_run_unit_tests --board=caroline --packages update_engine'

Change-Id: I14192b5ff9c07f8a003e0589450202f488cccc01
Reviewed-on: https://chromium-review.googlesource.com/1078968
Commit-Ready: Zentaro Kavanagh <zentaro@chromium.org>
Tested-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
diff --git a/metrics_reporter_omaha_unittest.cc b/metrics_reporter_omaha_unittest.cc
index c7641c0..ea72104 100644
--- a/metrics_reporter_omaha_unittest.cc
+++ b/metrics_reporter_omaha_unittest.cc
@@ -468,4 +468,26 @@
   reporter_.ReportInstallDateProvisioningSource(source, max);
 }
 
+TEST_F(MetricsReporterOmahaTest, ReportKeyVersionMetrics) {
+  int kernel_min_version = 0x00040002;
+  int kernel_max_rollforward_version = 0xfffffffe;
+  bool kernel_max_rollforward_success = true;
+  EXPECT_CALL(
+      *mock_metrics_lib_,
+      SendSparseToUMA(metrics::kMetricKernelMinVersion, kernel_min_version))
+      .Times(1);
+  EXPECT_CALL(*mock_metrics_lib_,
+              SendSparseToUMA(metrics::kMetricKernelMaxRollforwardVersion,
+                              kernel_max_rollforward_version))
+      .Times(1);
+  EXPECT_CALL(*mock_metrics_lib_,
+              SendBoolToUMA(metrics::kMetricKernelMaxRollforwardSetSuccess,
+                            kernel_max_rollforward_success))
+      .Times(1);
+
+  reporter_.ReportKeyVersionMetrics(kernel_min_version,
+                                    kernel_max_rollforward_version,
+                                    kernel_max_rollforward_success);
+}
+
 }  // namespace chromeos_update_engine