Fire webrtc log upload callback only when it is not null

Nested null callbacks can cause crashes.

Bug: 1090007
Change-Id: I967b0f1365ce4df1f489b595344bf247e2fac9df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2237890
Auto-Submit: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Marina Ciocea <marinaciocea@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776613}

chrome/browser/media/webrtc/webrtc_logging_controller.cc

@@ -491,10 +491,15 @@ void WebRtcLoggingController::DoUploadLogAndRtpDumps(
       base::UmaHistogramSparse("WebRtcTextLogging.UploadFailureReason",
                                WebRtcLogUploadFailureReason::kInvalidState);
     }
+
+    // Do not fire callback if it is null. Nesting null callbacks is not
+    // allowed, as it can lead to crashes. See https://crbug.com/1071475
+    if (callback.is_null())
+      return;
+
     base::SequencedTaskRunnerHandle::Get()->PostTask(
         FROM_HERE, base::BindOnce(callback, false, "",
                                   "Logging not stopped or no log open."));
-    return;
   }
 
   WebRtcLogUploader::UploadDoneData upload_done_data;