Add new Logger to iOS SDK to be able to intercept logs and report them to the appropriate system

Bug: webrtc:8695
Change-Id: I4f81529222dcaf3dded1a0ab93fabf5cda1fdef8
Reviewed-on: https://webrtc-review.googlesource.com/37001
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21821}

sdk/objc/Framework/Classes/Common/RTCCallbackLogger.mm

@@ -0,0 +1,84 @@
+/*
+ *  Copyright 2018 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/RTCCallbackLogger.h"
+
+#include <memory>
+
+#include "rtc_base/checks.h"
+#include "rtc_base/logging.h"
+#include "rtc_base/logsinks.h"
+
+class CallbackLogSink : public rtc::LogSink {
+ public:
+  CallbackLogSink(void (^callbackHandler)(NSString *message)) {
+    callback_handler_ = callbackHandler;
+  }
+
+  ~CallbackLogSink() override { callback_handler_ = nil; }
+
+  void OnLogMessage(const std::string &message) override {
+    if (callback_handler_) {
+      callback_handler_([NSString stringWithUTF8String:message.c_str()]);
+    }
+  }
+
+ private:
+  void (^callback_handler_)(NSString *message);
+};
+
+@implementation RTCCallbackLogger {
+  BOOL _hasStarted;
+  std::unique_ptr<CallbackLogSink> _logSink;
+}
+
+@synthesize severity = _severity;
+
+- (void)dealloc {
+  [self stop];
+}
+
+- (void)start:(nullable void (^)(NSString *))callback {
+  if (_hasStarted) {
+    return;
+  }
+
+  _logSink.reset(new CallbackLogSink(callback));
+
+  rtc::LogMessage::AddLogToStream(_logSink.get(), [self rtcSeverity]);
+  _hasStarted = YES;
+}
+
+- (void)stop {
+  if (!_hasStarted) {
+    return;
+  }
+  RTC_DCHECK(_logSink);
+  rtc::LogMessage::RemoveLogToStream(_logSink.get());
+  _hasStarted = NO;
+  _logSink.reset();
+}
+
+#pragma mark - Private
+
+- (rtc::LoggingSeverity)rtcSeverity {
+  switch (_severity) {
+    case RTCLoggingSeverityVerbose:
+      return rtc::LS_VERBOSE;
+    case RTCLoggingSeverityInfo:
+      return rtc::LS_INFO;
+    case RTCLoggingSeverityWarning:
+      return rtc::LS_WARNING;
+    case RTCLoggingSeverityError:
+      return rtc::LS_ERROR;
+  }
+}
+
+@end