Move the initialization of TabLifecycleUnitSource out of the constructor

On CrOS the global performance manager instance isn't available when
this gets created.

Change-Id: I082a1fae17665f10eab87a211157d4c969d1d238
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1704716Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678365}

chrome/browser/resource_coordinator/tab_lifecycle_unit_source.cc

@@ -116,10 +116,14 @@ TabLifecycleUnitSource::TabLifecycleUnitSource(
   // instantiated. No TabLifecycleUnit is created for these tabs.
 
   DCHECK(intervention_policy_database_);
+
   browser_tab_strip_tracker_.Init();
+}
+
+TabLifecycleUnitSource::~TabLifecycleUnitSource() = default;
 
-  auto* perf_man = performance_manager::PerformanceManager::GetInstance();
-  if (perf_man) {
+void TabLifecycleUnitSource::Start() {
+  if (auto* perf_man = performance_manager::PerformanceManager::GetInstance()) {
     // The performance manager dies on its own sequence, so posting unretained
     // is fine.
     perf_man->CallOnGraph(
@@ -133,8 +137,6 @@ TabLifecycleUnitSource::TabLifecycleUnitSource(
   }
 }
 
-TabLifecycleUnitSource::~TabLifecycleUnitSource() = default;
-
 // static
 TabLifecycleUnitExternal* TabLifecycleUnitSource::GetTabLifecycleUnitExternal(
     content::WebContents* web_contents) {

chrome/browser/resource_coordinator/tab_lifecycle_unit_source.h

@@ -46,6 +46,10 @@ class TabLifecycleUnitSource : public BrowserListObserver,
       UsageClock* usage_clock);
   ~TabLifecycleUnitSource() override;
 
+  // Should be called once all the dependencies of this class have been created
+  // (e.g. the global PerformanceManager instance).
+  void Start();
+
   // Returns the TabLifecycleUnitExternal instance associated with
   // |web_contents|, or nullptr if |web_contents| isn't a tab.
   static TabLifecycleUnitExternal* GetTabLifecycleUnitExternal(

chrome/browser/resource_coordinator/tab_manager.cc

@@ -35,6 +35,7 @@
 #include "chrome/browser/performance_manager/performance_manager.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/resource_coordinator/background_tab_navigation_throttle.h"
+#include "chrome/browser/resource_coordinator/resource_coordinator_parts.h"
 #include "chrome/browser/resource_coordinator/tab_lifecycle_unit_external.h"
 #include "chrome/browser/resource_coordinator/tab_manager.h"
 #include "chrome/browser/resource_coordinator/tab_manager_features.h"
@@ -222,6 +223,10 @@ void TabManager::Start() {
                        std::make_unique<ResourceCoordinatorSignalObserver>(
                            weak_ptr_factory_.GetWeakPtr())));
   }
+
+  g_browser_process->resource_coordinator_parts()
+      ->tab_lifecycle_unit_source()
+      ->Start();
 }
 
 LifecycleUnitVector TabManager::GetSortedLifecycleUnits() {