Background tracing: Disable when highres clock is not available

content/browser/tracing/background_tracing_manager_impl.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/tracing/background_tracing_manager_impl.h"
 
 #include "base/cpu.h"
 #include "base/json/json_writer.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 19 matching lines @@
 enum BackgroundTracingMetrics {
   SCENARIO_ACTIVATION_REQUESTED = 0,
   SCENARIO_ACTIVATED_SUCCESSFULLY = 1,
   RECORDING_ENABLED = 2,
   PREEMPTIVE_TRIGGERED = 3,
   REACTIVE_TRIGGERED = 4,
   FINALIZATION_ALLOWED = 5,
   FINALIZATION_DISALLOWED = 6,
   FINALIZATION_STARTED = 7,
   FINALIZATION_COMPLETE = 8,
+  SCENARIO_ACTION_FAILED_LOWRES_CLOCK = 9,
   NUMBER_OF_BACKGROUND_TRACING_METRICS,
 };
 
 void RecordBackgroundTracingMetric(BackgroundTracingMetrics metric) {
   UMA_HISTOGRAM_ENUMERATION("Tracing.Background.ScenarioState", metric,
                             NUMBER_OF_BACKGROUND_TRACING_METRICS);
 }
 
 std::string GetNetworkTypeString() {
   switch (net::NetworkChangeNotifier::GetConnectionType()) {
@@ skipping 75 matching lines @@
 bool BackgroundTracingManagerImpl::SetActiveScenario(
     scoped_ptr<BackgroundTracingConfig> config,
     const BackgroundTracingManager::ReceiveCallback& receive_callback,
     DataFiltering data_filtering) {
   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   RecordBackgroundTracingMetric(SCENARIO_ACTIVATION_REQUESTED);
 
   if (is_tracing_)
     return false;
 
+  // If we don't have a high resolution timer available, traces will be
+  // too inaccurate to be useful.
+  if (!base::TimeTicks::IsHighResolution()) {
+    RecordBackgroundTracingMetric(SCENARIO_ACTION_FAILED_LOWRES_CLOCK);
+    return false;
+  }
+
   bool requires_anonymized_data = (data_filtering == ANONYMIZE_DATA);
 
   // If the I/O thread isn't running, this is a startup scenario and
   // we have to wait until initialization is finished to validate that the
   // scenario can run.
   if (BrowserThread::IsThreadInitialized(BrowserThread::IO)) {
     // TODO(oysteine): Retry when time_until_allowed has elapsed.
     if (config && delegate_ &&
         !delegate_->IsAllowedToBeginBackgroundScenario(
             *config.get(), requires_anonymized_data)) {
@@ skipping 404 matching lines @@
     case BackgroundTracingConfigImpl::CategoryPreset::BENCHMARK_STARTUP:
       return "benchmark,toplevel,startup,disabled-by-default-file,"
              "disabled-by-default-toplevel.flow,"
              "disabled-by-default-ipc.flow";
   }
   NOTREACHED();
   return "";
 }
 
 }  // namspace content