diff --git a/metrics_constants.h b/metrics_constants.h
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+//
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef UPDATE_ENGINE_METRICS_CONSTANTS_H_
+#define UPDATE_ENGINE_METRICS_CONSTANTS_H_
+
+namespace chromeos_update_engine {
+
+namespace metrics {
+// The possible outcomes when checking for updates.
+//
+// This is used in the UpdateEngine.Check.Result histogram.
+enum class CheckResult {
+  kUpdateAvailable,    // Response indicates an update is available.
+  kNoUpdateAvailable,  // Response indicates no updates are available.
+  kDownloadError,      // Error downloading response from Omaha.
+  kParsingError,       // Error parsing response.
+  kRebootPending,      // No update check was performed a reboot is pending.
+
+  kNumConstants,
+  kUnset = -1
+};
+
+// Possible ways a device can react to a new update being available.
+//
+// This is used in the UpdateEngine.Check.Reaction histogram.
+enum class CheckReaction {
+  kUpdating,    // Device proceeds to download and apply update.
+  kIgnored,     // Device-policy dictates ignoring the update.
+  kDeferring,   // Device-policy dictates waiting.
+  kBackingOff,  // Previous errors dictates waiting.
+
+  kNumConstants,
+  kUnset = -1
+};
+
+// The possible ways that downloading from a HTTP or HTTPS server can fail.
+//
+// This is used in the UpdateEngine.Check.DownloadErrorCode and
+// UpdateEngine.Attempt.DownloadErrorCode histograms.
+enum class DownloadErrorCode {
+  // Errors that can happen in the field. See http://crbug.com/355745
+  // for how we plan to add more detail in the future.
+  kDownloadError = 0,  // Error downloading data from server.
+
+  // IMPORTANT: When adding a new error code, add at the bottom of the
+  // above block and before the kInputMalformed field. This
+  // is to ensure that error codes are not reordered.
+
+  // This error code is used to convey that malformed input was given
+  // to the utils::GetDownloadErrorCode() function. This should never
+  // happen but if it does it's because of an internal update_engine
+  // error and we're interested in knowing this.
+  kInputMalformed = 100,
+
+  // Bucket for capturing HTTP status codes not in the 200-599
+  // range. This should never happen in practice but if it does we
+  // want to know.
+  kHttpStatusOther = 101,
+
+  // Above 200 and below 600, the value is the HTTP status code.
+  kHttpStatus200 = 200,
+
+  kNumConstants = 600,
+
+  kUnset = -1
+};
+
+// Possible ways an update attempt can end.
+//
+// This is used in the UpdateEngine.Attempt.Result histogram.
+enum class AttemptResult {
+  kUpdateSucceeded,             // The update succeeded.
+  kInternalError,               // An internal error occurred.
+  kPayloadDownloadError,        // Failure while downloading payload.
+  kMetadataMalformed,           // Metadata was malformed.
+  kOperationMalformed,          // An operation was malformed.
+  kOperationExecutionError,     // An operation failed to execute.
+  kMetadataVerificationFailed,  // Metadata verification failed.
+  kPayloadVerificationFailed,   // Payload verification failed.
+  kVerificationFailed,          // Root or Kernel partition verification failed.
+  kPostInstallFailed,           // The postinstall step failed.
+  kAbnormalTermination,         // The attempt ended abnormally.
+  kUpdateCanceled,              // Update canceled by the user.
+
+  kNumConstants,
+
+  kUnset = -1
+};
+
+// Possible ways the device is connected to the Internet.
+//
+// This is used in the UpdateEngine.Attempt.ConnectionType histogram.
+enum class ConnectionType {
+  kUnknown,           // Unknown.
+  kEthernet,          // Ethernet.
+  kWifi,              // Wireless.
+  kWimax,             // WiMax.
+  kBluetooth,         // Bluetooth.
+  kCellular,          // Cellular.
+  kTetheredEthernet,  // Tethered (Ethernet).
+  kTetheredWifi,      // Tethered (Wifi).
+
+  kNumConstants,
+  kUnset = -1
+};
+
+// Possible ways a rollback can end.
+//
+// This is used in the UpdateEngine.Rollback histogram.
+enum class RollbackResult {
+  kFailed,
+  kSuccess,
+
+  kNumConstants
+};
+
+}  // namespace metrics
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_METRICS_CONSTANTS_H_