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

BUG=webrtc:7868

Review-Url: https://codereview.webrtc.org/2961663002
Cr-Commit-Position: refs/heads/master@{#18933}

webrtc/rtc_base/event_tracer.cc

@@ -374,10 +374,15 @@ void SetupInternalTracer() {
 }
 
 void StartInternalCaptureToFile(FILE* file) {
-  g_event_logger->Start(file, false);
+  if (g_event_logger) {
+    g_event_logger->Start(file, false);
+  }
 }
 
 bool StartInternalCapture(const char* filename) {
+  if (!g_event_logger)
+    return false;
+
   FILE* file = fopen(filename, "w");
   if (!file) {
     LOG(LS_ERROR) << "Failed to open trace file '" << filename
@@ -389,7 +394,9 @@ bool StartInternalCapture(const char* filename) {
 }
 
 void StopInternalCapture() {
-  g_event_logger->Stop();
+  if (g_event_logger) {
+    g_event_logger->Stop();
+  }
 }
 
 void ShutdownInternalTracer() {

webrtc/sdk/BUILD.gn

@@ -510,6 +510,7 @@ if (is_ios || is_mac) {
           "objc/Framework/UnitTests/RTCMediaConstraintsTest.mm",
           "objc/Framework/UnitTests/RTCPeerConnectionTest.mm",
           "objc/Framework/UnitTests/RTCSessionDescriptionTest.mm",
+          "objc/Framework/UnitTests/RTCTracingTest.mm",
           "objc/Framework/UnitTests/avformatmappertests.mm",
         ]
         if (is_ios &&

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

@@ -0,0 +1,50 @@
+/*
+ *  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];
+  }
+}
+