bluetooth: Create bluetooth_metrics_hash tool.

content/browser/bluetooth/bluetooth_metrics.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/bluetooth/bluetooth_metrics.h"
 
 #include <stdint.h>
 
 #include <map>
 #include <set>
 #include "base/hash.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
 #include "content/common/bluetooth/bluetooth_scan_filter.h"
 #include "device/bluetooth/bluetooth_uuid.h"
 
 using device::BluetoothUUID;
 
 namespace {
-// TODO(ortuno): Remove once we have a macro to histogram strings.
-// http://crbug.com/520284
-int HashUUID(const std::string& uuid) {
-  uint32_t data = base::SuperFastHash(uuid.data(), uuid.size());
 
-  // Strip off the signed bit because UMA doesn't support negative values,
+// Generates a hash from a canonical UUID string suitable for
+// UMA_HISTOGRAM_SPARSE_SLOWLY (positive int).
+//
+// Hash values can be produced manually using tool: bluetooth_metrics_hash.
+int HashUUID(const std::string& canonical_uuid) {
+  DCHECK(canonical_uuid == BluetoothUUID(canonical_uuid).canonical_value());
+
+  // TODO(520284): Other than verifying that uuid is canonical, this logic
+  // should be migrated to a dedicated histogram macro for hashed strings.
+  uint32_t data =
+      base::SuperFastHash(canonical_uuid.data(), canonical_uuid.size());
+
+  // Strip off the sign bit because UMA doesn't support negative values,
   // but takes a signed int as input.
   return static_cast<int>(data & 0x7fffffff);
 }
 }  // namespace
 
 namespace content {
 
 // General
 
 void RecordWebBluetoothFunctionCall(UMAWebBluetoothFunction function) {
@@ skipping 240 matching lines @@
       static_cast<int>(outcome),
       static_cast<int>(UMAGATTOperationOutcome::COUNT));
 }
 
 void RecordStartNotificationsOutcome(CacheQueryOutcome outcome) {
   RecordStartNotificationsOutcome(
       TranslateCacheQueryOutcomeToGATTOperationOutcome(outcome));
 }
 
 }  // namespace content