Make memory pressure notifier configurable

base/memory/memory_pressure_monitor_chromeos.cc

Index: base/memory/memory_pressure_monitor_chromeos.cc
diff --git a/base/memory/memory_pressure_monitor_chromeos.cc b/base/memory/memory_pressure_monitor_chromeos.cc
index 2d0b0a62fc6d7c1dbbb77aa98f06132d5f93a966..22495dfc5ca07b9978f9b4f76bb4a2b4fa35e59e 100644
--- a/base/memory/memory_pressure_monitor_chromeos.cc
+++ b/base/memory/memory_pressure_monitor_chromeos.cc
@@ -230,7 +230,7 @@ void MemoryPressureMonitor::CheckMemoryPressure() {
     return;
   }
   moderate_pressure_repeat_count_ = 0;
-  MemoryPressureListener::NotifyMemoryPressure(current_memory_pressure_level_);
+  Notify(current_memory_pressure_level_);
 }
 
 // Gets the used ChromeOS memory in percent.
@@ -271,5 +271,19 @@ int MemoryPressureMonitor::GetUsedMemoryInPercent() {
   return percentage;
 }
 
+void MemoryPressureMonitor::SetObserver(
+    MemoryPressureMonitorObserver* observer) {
+  DCHECK(!observer_);
+  observer_ = observer;
+}
+
+void MemoryPressureMonitor::Notify(MemoryPressureLevel level) {
+  if (observer_) {
+    observer_->OnMemoryPressure(level);
+  } else {
+    base::MemoryPressureListener::NotifyMemoryPressure(level);
+  }
+}
+
 }  // namespace chromeos
 }  // namespace base