Whitelist arguments for ScopedThreadMayLoadLibraryOnBackgroundThread

Add arguments from ScopedThreadMayLoadLibraryOnBackgroundThread to the
tracing whitelist.

ScopedThreadMayLoadLibraryOnBackgroundThread::
    ScopedThreadMayLoadLibraryOnBackgroundThread(const Location& from_here) {

  TRACE_EVENT_BEGIN2("base", "ScopedThreadMayLoadLibraryOnBackgroundThread",
                     "file_name", from_here.file_name(), "function_name",
                     from_here.function_name());
  [...]
}

R=oysteine@chromium.org

Bug: 973868
Change-Id: If6bfa7c224a4c69c9d004526c773ad0d69534ea5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1773702Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691735}

services/tracing/public/cpp/trace_event_args_whitelist.cc

@@ -50,6 +50,8 @@ const WhitelistEntry kEventArgsWhitelist[] = {
     {"__metadata", "stackFrames", nullptr},
     {"__metadata", "typeNames", nullptr},
     {"base", "ScopedBlockingCall*", kScopedBlockingCallAllowedArgs},
+    {"base", "ScopedThreadMayLoadLibraryOnBackgroundThread",
+     kScopedBlockingCallAllowedArgs},
     {"benchmark", "TestWhitelist*", nullptr},
     {"browser", "KeyedServiceFactory::GetServiceForContext", nullptr},
     {"fonts", "CachedFontLinkSettings::GetLinkedFonts", nullptr},