Background Tracing: Remove safety check for crash exit on Android

On Android the exit status is always marked as EXIT_CRASHED. So, the
background traces are never uploaded. Since the check is useful only for
preemptive mode, this CL removes this check for REACTIVE triggers on
Android and adds extra check for preemptive trigger in that place.

BUG=613198

Review-Url: https://codereview.chromium.org/2192093002
Cr-Commit-Position: refs/heads/master@{#408771}

chrome/browser/tracing/chrome_tracing_delegate.cc

@@ -84,10 +84,17 @@ bool ProfileAllowsScenario(const content::BackgroundTracingConfig& config,
       return true;
   }
 
+#if !defined(OS_ANDROID)
   // Safeguard, in case background tracing is responsible for a crash on
   // startup.
   if (profile->GetLastSessionExitType() == Profile::EXIT_CRASHED)
     return false;
+#else
+  // In case of Android the exit state is always set as EXIT_CRASHED. So,
+  // preemptive mode cannot be used safely.
+  if (config.tracing_mode() == content::BackgroundTracingConfig::PREEMPTIVE)
+    return false;
+#endif
 
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);