Make memory pressure notifier configurable

base/memory/memory_pressure_monitor_win.cc

Index: base/memory/memory_pressure_monitor_win.cc
diff --git a/base/memory/memory_pressure_monitor_win.cc b/base/memory/memory_pressure_monitor_win.cc
index 8ac66cec0880248cdea7107cd2c6b33806e4cdf4..8052812d98db2ef527dc885fffb170a4dea0bc39 100644
--- a/base/memory/memory_pressure_monitor_win.cc
+++ b/base/memory/memory_pressure_monitor_win.cc
@@ -198,7 +198,7 @@ void MemoryPressureMonitor::CheckMemoryPressure() {
   // happen for moderate and critical pressure levels.
   DCHECK_NE(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
             current_memory_pressure_level_);
-  MemoryPressureListener::NotifyMemoryPressure(current_memory_pressure_level_);
+  Notify(current_memory_pressure_level_);
 }
 
 void MemoryPressureMonitor::CheckMemoryPressureAndRecordStatistics() {
@@ -250,5 +250,19 @@ bool MemoryPressureMonitor::GetSystemMemoryStatus(
   return true;
 }
 
+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 win
 }  // namespace base