Background tracing: Tracing scenarios can now enable/disable Blink features, for A/B testing purpos…

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/command_line.h"
 #include "base/cpu.h"
 #include "base/json/json_writer.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/sys_info.h"
 #include "base/time/time.h"
 #include "content/browser/tracing/background_tracing_rule.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/gpu_data_manager.h"
 #include "content/public/browser/tracing_delegate.h"
 #include "content/public/common/content_client.h"
+#include "content/public/common/content_switches.h"
 #include "gpu/config/gpu_info.h"
 #include "net/base/network_change_notifier.h"
 
 namespace content {
 
 namespace {
 
 base::LazyInstance<BackgroundTracingManagerImpl>::Leaky g_controller =
     LAZY_INSTANCE_INITIALIZER;
 
@@ skipping 115 matching lines @@
             *config.get(), requires_anonymized_data)) {
       return false;
     }
   } else {
     base::MessageLoop::current()->PostTask(
         FROM_HERE,
         base::Bind(&BackgroundTracingManagerImpl::ValidateStartupScenario,
                    base::Unretained(this)));
   }
 
-  // No point in tracing if there's nowhere to send it.
-  if (config && receive_callback.is_null())
-    return false;
+  scoped_ptr<const content::BackgroundTracingConfigImpl> config_impl(
+      static_cast<BackgroundTracingConfigImpl*>(config.release()));
 
-  config_.reset(static_cast<BackgroundTracingConfigImpl*>(config.release()));
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+
+  if (config_impl) {
+    // No point in tracing if there's nowhere to send it.
+    if (receive_callback.is_null())
+      return false;
+
+    // If the scenario requires us to toggle Blink features, we want
+    // to neither override anything else nor to do we want to activate
+    // the scenario without doing the toggle, so if something else has
+    // configured these switches we just abort.
+    if (!config_impl->enable_blink_features().empty() &&
+        command_line->HasSwitch(switches::kEnableBlinkFeatures)) {
+      return false;
+    }
+
+    if (!config_impl->disable_blink_features().empty() &&
+        command_line->HasSwitch(switches::kDisableBlinkFeatures)) {
+      return false;
+    }
+  }
+
+  config_ = config_impl.Pass();
   receive_callback_ = receive_callback;
   requires_anonymized_data_ = requires_anonymized_data;
 
   if (config_) {
     DCHECK(!config_.get()->rules().empty());
     for (auto& rule : config_.get()->rules())
       static_cast<BackgroundTracingRule*>(rule)->Install();
+
+    if (!config_->enable_blink_features().empty()) {
+      command_line->AppendSwitchASCII(switches::kEnableBlinkFeatures,
+                                      config_->enable_blink_features());
+    }
+
+    if (!config_->disable_blink_features().empty()) {
+      command_line->AppendSwitchASCII(switches::kDisableBlinkFeatures,
+                                      config_->disable_blink_features());
+    }
   }
 
   EnableRecordingIfConfigNeedsIt();
 
   RecordBackgroundTracingMetric(SCENARIO_ACTIVATED_SUCCESSFULLY);
   return true;
 }
 
 bool BackgroundTracingManagerImpl::HasActiveScenarioForTesting() {
   return config_;
@@ skipping 373 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