Make memory pressure notifier configurable

base/memory/memory_pressure_monitor_mac.cc

Index: base/memory/memory_pressure_monitor_mac.cc
diff --git a/base/memory/memory_pressure_monitor_mac.cc b/base/memory/memory_pressure_monitor_mac.cc
index ec807eeec32e02fc3de28ce434f633bb7909e1c4..4e37ff950df5eaad44071d3cb93be2d136110dcc 100644
--- a/base/memory/memory_pressure_monitor_mac.cc
+++ b/base/memory/memory_pressure_monitor_mac.cc
@@ -8,6 +8,7 @@
 #include <stddef.h>
 #include <sys/sysctl.h>
 
+#include "base/logging.h"
 #include "base/mac/mac_util.h"
 
 // Redeclare for partial 10.9 availability.
@@ -32,11 +33,11 @@ MemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressure(
 }
 
 void MemoryPressureMonitor::NotifyMemoryPressureChanged(
-    dispatch_source_s* event_source) {
+    dispatch_source_s* event_source, MemoryPressureMonitor* monitor) {
   int mac_memory_pressure = dispatch_source_get_data(event_source);
   MemoryPressureListener::MemoryPressureLevel memory_pressure_level =
       MemoryPressureLevelForMacMemoryPressure(mac_memory_pressure);
-  MemoryPressureListener::NotifyMemoryPressure(memory_pressure_level);
+  monitor->Notify(memory_pressure_level);
 }
 
 MemoryPressureMonitor::MemoryPressureMonitor()
@@ -49,7 +50,7 @@ MemoryPressureMonitor::MemoryPressureMonitor()
           DISPATCH_MEMORYPRESSURE_WARN | DISPATCH_MEMORYPRESSURE_CRITICAL,
           dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0))) {
   dispatch_source_set_event_handler(memory_level_event_source_, ^{
-    NotifyMemoryPressureChanged(memory_level_event_source_.get());
+    NotifyMemoryPressureChanged(memory_level_event_source_.get(), this);
   });
   dispatch_resume(memory_level_event_source_);
 }
@@ -67,5 +68,19 @@ MemoryPressureMonitor::GetCurrentPressureLevel() const {
   return MemoryPressureLevelForMacMemoryPressure(mac_memory_pressure);
 }
 
+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 mac
 }  // namespace base