Reland of Add EnabledStateObserver to BackgroundTracingManager

content/browser/tracing/background_tracing_manager_impl.h

Index: content/browser/tracing/background_tracing_manager_impl.h
diff --git a/content/browser/tracing/background_tracing_manager_impl.h b/content/browser/tracing/background_tracing_manager_impl.h
index 637c70d0b51d26893b38fe3c380599706016608e..4e329a3f978c35173b61a03026a0b7a1bdcb998f 100644
--- a/content/browser/tracing/background_tracing_manager_impl.h
+++ b/content/browser/tracing/background_tracing_manager_impl.h
@@ -23,7 +23,24 @@ class TracingDelegate;
 
 class BackgroundTracingManagerImpl : public BackgroundTracingManager {
  public:
-  static CONTENT_EXPORT BackgroundTracingManagerImpl* GetInstance();
+  // Enabled state observers get a callback when the state of background tracing
+  // changes.
+  class CONTENT_EXPORT EnabledStateObserver {
+   public:
+    // Called when the activation of a background tracing scenario is
+    // successful.
+    virtual void OnScenarioActivated(
+        const BackgroundTracingConfigImpl* config) = 0;
+
+    // Called after tracing is enabled on all processes because the rule was
+    // triggered.
+    virtual void OnTracingEnabled(
+        BackgroundTracingConfigImpl::CategoryPreset preset) = 0;
+
+    virtual ~EnabledStateObserver() = default;
+  };
+
+  CONTENT_EXPORT static BackgroundTracingManagerImpl* GetInstance();
 
   bool SetActiveScenario(std::unique_ptr<BackgroundTracingConfig>,
                          const ReceiveCallback&,
@@ -40,10 +57,15 @@ class BackgroundTracingManagerImpl : public BackgroundTracingManager {
   void AbortScenario();
   bool HasActiveScenario() override;
 
+  void OnStartTracingDone(BackgroundTracingConfigImpl::CategoryPreset preset);
+
+  // Add/remove EnabledStateObserver.
+  CONTENT_EXPORT void AddEnabledStateObserver(EnabledStateObserver* observer);
+  CONTENT_EXPORT void RemoveEnabledStateObserver(
+      EnabledStateObserver* observer);
+
   // For tests
   void InvalidateTriggerHandlesForTesting() override;
-  void SetTracingEnabledCallbackForTesting(
-      const base::Closure& callback) override;
   CONTENT_EXPORT void SetRuleTriggeredCallbackForTesting(
       const base::Closure& callback);
   void FireTimerForTesting() override;
@@ -103,6 +125,8 @@ class BackgroundTracingManagerImpl : public BackgroundTracingManager {
 
   TriggerHandle triggered_named_event_handle_;
 
+  std::vector<EnabledStateObserver*> background_tracing_observer_list_;
+
   IdleCallback idle_callback_;
   base::Closure tracing_enabled_callback_for_testing_;
   base::Closure rule_triggered_callback_for_testing_;