Add default implementations for LifecycleUnitObserver methods.

These will be useful for an upcoming CL were TabManager doesn't need
to have its own implementation of all methods.

Bug: 775644
Change-Id: Id746ab0fbf821cc7c20be731c3e84950ae470631
Reviewed-on: https://chromium-review.googlesource.com/981263Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547149}

chrome/browser/BUILD.gn

@@ -2617,6 +2617,7 @@ jumbo_split_static_library("browser") {
       "resource_coordinator/lifecycle_unit.h",
       "resource_coordinator/lifecycle_unit_base.cc",
       "resource_coordinator/lifecycle_unit_base.h",
+      "resource_coordinator/lifecycle_unit_observer.cc",
       "resource_coordinator/lifecycle_unit_observer.h",
       "resource_coordinator/lifecycle_unit_source.h",
       "resource_coordinator/lifecycle_unit_source_base.cc",

chrome/browser/resource_coordinator/discard_metrics_lifecycle_unit_observer.cc

@@ -25,10 +25,6 @@ void DiscardMetricsLifecycleUnitObserver::OnLifecycleUnitStateChanged(
     OnReload();
 }
 
-void DiscardMetricsLifecycleUnitObserver::OnLifecycleUnitVisibilityChanged(
-    LifecycleUnit* lifecycle_unit,
-    content::Visibility visibility) {}
-
 void DiscardMetricsLifecycleUnitObserver::OnLifecycleUnitDestroyed(
     LifecycleUnit* lifecycle_unit) {
   // If the browser is not shutting down and the tab is in a LOADED state after

chrome/browser/resource_coordinator/discard_metrics_lifecycle_unit_observer.h

@@ -20,9 +20,6 @@ class DiscardMetricsLifecycleUnitObserver : public LifecycleUnitObserver {
 
   // LifecycleUnitObserver:
   void OnLifecycleUnitStateChanged(LifecycleUnit* lifecycle_unit) override;
-  void OnLifecycleUnitVisibilityChanged(
-      LifecycleUnit* lifecycle_unit,
-      content::Visibility visibility) override;
   void OnLifecycleUnitDestroyed(LifecycleUnit* lifecycle_unit) override;
 
  private:

chrome/browser/resource_coordinator/lifecycle_unit_observer.cc

+// Copyright 2018 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 "chrome/browser/resource_coordinator/lifecycle_unit_observer.h"
+
+namespace resource_coordinator {
+
+LifecycleUnitObserver::~LifecycleUnitObserver() = default;
+
+void LifecycleUnitObserver::OnLifecycleUnitStateChanged(
+    LifecycleUnit* lifecycle_unit) {}
+
+void LifecycleUnitObserver::OnLifecycleUnitVisibilityChanged(
+    LifecycleUnit* lifecycle_unit,
+    content::Visibility visibility) {}
+
+void LifecycleUnitObserver::OnLifecycleUnitDestroyed(
+    LifecycleUnit* lifecycle_unit) {}
+
+}  // namespace resource_coordinator

chrome/browser/resource_coordinator/lifecycle_unit_observer.h

@@ -14,19 +14,18 @@ class LifecycleUnit;
 // Interface to be notified when the state of a LifecycleUnit changes.
 class LifecycleUnitObserver {
  public:
-  virtual ~LifecycleUnitObserver() = default;
+  virtual ~LifecycleUnitObserver();
 
   // Invoked when the state of the observed LifecycleUnit changes.
-  virtual void OnLifecycleUnitStateChanged(LifecycleUnit* lifecycle_unit) = 0;
+  virtual void OnLifecycleUnitStateChanged(LifecycleUnit* lifecycle_unit);
 
   // Invoked when the visibility of the observed LifecyleUnit changes.
-  virtual void OnLifecycleUnitVisibilityChanged(
-      LifecycleUnit* lifecycle_unit,
-      content::Visibility visibility) = 0;
+  virtual void OnLifecycleUnitVisibilityChanged(LifecycleUnit* lifecycle_unit,
+                                                content::Visibility visibility);
 
   // Invoked before the observed LifecycleUnit starts being destroyed (i.e.
   // |lifecycle_unit| is still valid when this is invoked).
-  virtual void OnLifecycleUnitDestroyed(LifecycleUnit* lifecycle_unit) = 0;
+  virtual void OnLifecycleUnitDestroyed(LifecycleUnit* lifecycle_unit);
 };
 
 }  // namespace resource_coordinator