Add ObjC API for getting native histograms.

BUG=

Review-Url: https://codereview.webrtc.org/2036773003
Cr-Commit-Position: refs/heads/master@{#13064}

webrtc/sdk/objc/Framework/Classes/RTCMetrics.mm

@@ -0,0 +1,32 @@
+/*
+ *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#import "WebRTC/RTCMetrics.h"
+
+#import "RTCMetricsSampleInfo+Private.h"
+
+void RTCEnableMetrics() {
+  webrtc::metrics::Enable();
+}
+
+NSArray<RTCMetricsSampleInfo *> *RTCGetAndResetMetrics() {
+  std::map<std::string, std::unique_ptr<webrtc::metrics::SampleInfo>>
+      histograms;
+  webrtc::metrics::GetAndReset(&histograms);
+
+  NSMutableArray *metrics =
+      [NSMutableArray arrayWithCapacity:histograms.size()];
+  for (auto const &histogram : histograms) {
+    RTCMetricsSampleInfo *metric = [[RTCMetricsSampleInfo alloc]
+        initWithNativeSampleInfo:*histogram.second];
+    [metrics addObject:metric];
+  }
+  return metrics;
+}