Add ObjC API for getting native histograms.

BUG=

Review-Url: https://codereview.webrtc.org/2036773003
Cr-Commit-Position: refs/heads/master@{#13064}
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCMetrics.mm b/webrtc/sdk/objc/Framework/Classes/RTCMetrics.mm
new file mode 100644
index 0000000..279a2be
--- /dev/null
+++ b/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;
+}
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo+Private.h b/webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo+Private.h
new file mode 100644
index 0000000..00d3fa6
--- /dev/null
+++ b/webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo+Private.h
@@ -0,0 +1,25 @@
+/*
+ *  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/RTCMetricsSampleInfo.h"
+
+#include "webrtc/system_wrappers/include/metrics_default.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCMetricsSampleInfo ()
+
+/** Initialize an RTCMetricsSampleInfo object from native SampleInfo. */
+- (instancetype)initWithNativeSampleInfo:
+    (const webrtc::metrics::SampleInfo &)info;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo.mm b/webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo.mm
new file mode 100644
index 0000000..628ba9e
--- /dev/null
+++ b/webrtc/sdk/objc/Framework/Classes/RTCMetricsSampleInfo.mm
@@ -0,0 +1,43 @@
+/*
+ *  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 "RTCMetricsSampleInfo+Private.h"
+
+#import "NSString+StdString.h"
+
+@implementation RTCMetricsSampleInfo
+
+@synthesize name = _name;
+@synthesize min = _min;
+@synthesize max = _max;
+@synthesize bucketCount = _bucketCount;
+@synthesize samples = _samples;
+
+#pragma mark - Private
+
+- (instancetype)initWithNativeSampleInfo:
+    (const webrtc::metrics::SampleInfo &)info {
+  if (self = [super init]) {
+    _name = [NSString stringForStdString:info.name];
+    _min = info.min;
+    _max = info.max;
+    _bucketCount = info.bucket_count;
+
+    NSMutableDictionary *samples =
+        [NSMutableDictionary dictionaryWithCapacity:info.samples.size()];
+    for (auto const &sample : info.samples) {
+      [samples setObject:@(sample.second) forKey:@(sample.first)];
+    }
+    _samples = samples;
+  }
+  return self;
+}
+
+@end