[aw][tracing] Set up bg tracing on startup

This change adds code to enable background tracing in WebView under the
following conditions:
- system tracing is configured
- the config specifies system tracing mode.

Bug: b/170513316
Change-Id: I5a38255a0098d3d91bbdd33facb23df5c9c8f2c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2508312
Commit-Queue: Oksana Zhuravlova <oksamyt@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Michael Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823759}

android_webview/browser/BUILD.gn

@@ -170,6 +170,8 @@ source_set("browser") {
     "tracing/aw_tracing_controller.h",
     "tracing/aw_tracing_delegate.cc",
     "tracing/aw_tracing_delegate.h",
+    "tracing/background_tracing_field_trial.cc",
+    "tracing/background_tracing_field_trial.h",
   ]
 
   deps = [

android_webview/browser/DEPS

@@ -79,6 +79,9 @@ include_rules = [
   "+mojo/core/embedder/embedder.h",
   "+mojo/public/cpp/system",
 
+  # Background tracing support
+  "+services/tracing/public/cpp",
+
   "+storage/browser/quota",
   "+storage/common/quota",
 

android_webview/browser/aw_browser_main_parts.cc

@@ -15,6 +15,7 @@
 #include "android_webview/browser/aw_web_ui_controller_factory.h"
 #include "android_webview/browser/metrics/aw_metrics_service_client.h"
 #include "android_webview/browser/network_service/aw_network_change_notifier_factory.h"
+#include "android_webview/browser/tracing/background_tracing_field_trial.h"
 #include "android_webview/common/aw_descriptors.h"
 #include "android_webview/common/aw_paths.h"
 #include "android_webview/common/aw_resource.h"
@@ -141,6 +142,8 @@ void AwBrowserMainParts::PostCreateThreads() {
   heap_profiling::Mode mode = heap_profiling::GetModeForStartup();
   if (mode != heap_profiling::Mode::kNone)
     heap_profiling::Supervisor::GetInstance()->Start(base::NullCallback());
+
+  SetupBackgroundTracingFieldTrial();
 }
 
 }  // namespace android_webview

android_webview/browser/tracing/background_tracing_field_trial.cc

+// Copyright 2020 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 "android_webview/browser/tracing/background_tracing_field_trial.h"
+
+#include "base/bind_helpers.h"
+#include "content/public/browser/background_tracing_config.h"
+#include "content/public/browser/background_tracing_manager.h"
+#include "services/tracing/public/cpp/tracing_features.h"
+
+namespace android_webview {
+
+void SetupBackgroundTracingFieldTrial() {
+  std::unique_ptr<content::BackgroundTracingConfig> config =
+      content::BackgroundTracingManager::GetInstance()
+          ->GetBackgroundTracingConfig();
+
+  if (config &&
+      config->tracing_mode() == content::BackgroundTracingConfig::SYSTEM &&
+      tracing::ShouldSetupSystemTracing()) {
+    // Only enable background tracing for system tracing if the system producer
+    // is enabled.
+    content::BackgroundTracingManager::GetInstance()->SetActiveScenario(
+        std::move(config),
+        base::BindRepeating(
+            base::DoNothing::Repeatedly<std::unique_ptr<std::string>,
+                                        content::BackgroundTracingManager::
+                                            FinishedProcessingCallback>()),
+        content::BackgroundTracingManager::ANONYMIZE_DATA);
+  }
+}
+
+}  // namespace android_webview
\ No newline at end of file

android_webview/browser/tracing/background_tracing_field_trial.h

+// Copyright 2020 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.
+
+#ifndef ANDROID_WEBVIEW_BROWSER_TRACING_BACKGROUND_TRACING_FIELD_TRIAL_H_
+#define ANDROID_WEBVIEW_BROWSER_TRACING_BACKGROUND_TRACING_FIELD_TRIAL_H_
+
+namespace android_webview {
+
+void SetupBackgroundTracingFieldTrial();
+
+}  // namespace android_webview
+
+#endif  // ANDROID_WEBVIEW_BROWSER_TRACING_BACKGROUND_TRACING_FIELD_TRIAL_H_