Background tracing: Enable preemptive mode on android

Change-Id: I49e26e74aeff801873b5e40a757c1042dc79fd4c
Reviewed-on: https://chromium-review.googlesource.com/c/1321949Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: ssid <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606153}

chrome/browser/tracing/chrome_tracing_delegate.cc

@@ -162,12 +162,6 @@ bool ProfileAllowsScenario(const content::BackgroundTracingConfig& config,
 bool ChromeTracingDelegate::IsAllowedToBeginBackgroundScenario(
     const content::BackgroundTracingConfig& config,
     bool requires_anonymized_data) {
-#if defined(OS_ANDROID)
-  // TODO(oysteine): Support preemptive mode safely in Android.
-  if (config.tracing_mode() == content::BackgroundTracingConfig::PREEMPTIVE)
-    return false;
-#endif
-
   if (!ProfileAllowsScenario(config, PROFILE_NOT_REQUIRED))
     return false;