Trace loggging: Check for g_event_logger is not null before calling it.

webrtc/sdk/objc/Framework/UnitTests/RTCTracingTest.mm

+/*
+ *  Copyright 2017 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 <Foundation/Foundation.h>
+
+#include <vector>
+
+#include "webrtc/base/gunit.h"
+
+#import "NSString+StdString.h"
+#import "WebRTC/RTCTracing.h"
+
+@interface RTCTracingTest : NSObject
+- (void)tracingTestNoInitialization;
+@end
+
+@implementation RTCTracingTest
+
+- (NSString *)documentsFilePathForFileName:(NSString *)fileName {
+  NSParameterAssert(fileName.length);
+  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
+  NSString *documentsDirPath = paths.firstObject;
+  NSString *filePath =
+  [documentsDirPath stringByAppendingPathComponent:fileName];
+  return filePath;
+}
+
+- (void)tracingTestNoInitialization {
+  NSString *filePath = [self documentsFilePathForFileName:@"webrtc-trace.txt"];
+  EXPECT_EQ(NO, RTCStartInternalCapture(filePath));
+  RTCStopInternalCapture();
+}
+
+@end
+
+
+TEST(RTCTracingTest, TracingTestNoInitialization) {
+  @autoreleasepool {
+    RTCTracingTest *test = [[RTCTracingTest alloc] init];
+    [test tracingTestNoInitialization];
+  }
+}
+