Do V8 GC ASAP if system memory is pressured

base/memory/memory_pressure_listener.cc

Index: base/memory/memory_pressure_listener.cc
diff --git a/base/memory/memory_pressure_listener.cc b/base/memory/memory_pressure_listener.cc
index 9fd675aa4e52a0dd679c0d26456da990c31589d3..19a074ab2c4a2ad188fad4de084305ac32d256d7 100644
--- a/base/memory/memory_pressure_listener.cc
+++ b/base/memory/memory_pressure_listener.cc
@@ -44,6 +44,14 @@ MemoryPressureListener::MemoryPressureListener(
   g_observers.Get().AddObserver(this);
 }
 
+MemoryPressureListener::MemoryPressureListener(
+    const MemoryPressureListener::MemoryPressureCallback& callback,
+    const MemoryPressureListener::SyncMemoryPressuredCallback& sync_callback)
+    : callback_(callback),
+      sync_memory_pressured_callback_(sync_callback) {
+  g_observers.Get().AddObserver(this);
+}
+
 MemoryPressureListener::~MemoryPressureListener() {
   g_observers.Get().RemoveObserver(this);
 }
@@ -52,6 +60,13 @@ void MemoryPressureListener::Notify(MemoryPressureLevel memory_pressure_level) {
   callback_.Run(memory_pressure_level);
 }
 
+void MemoryPressureListener::SyncNotify(
+    MemoryPressureLevel memory_pressure_level) {
+  if (!sync_memory_pressured_callback_.is_null()) {
+    sync_memory_pressured_callback_.Run(true);
+  }
+}
+
 // static
 void MemoryPressureListener::NotifyMemoryPressure(
     MemoryPressureLevel memory_pressure_level) {
@@ -84,6 +99,9 @@ void MemoryPressureListener::SimulatePressureNotification(
 void MemoryPressureListener::DoNotifyMemoryPressure(
     MemoryPressureLevel memory_pressure_level) {
   DCHECK_NE(memory_pressure_level, MEMORY_PRESSURE_LEVEL_NONE);
+
+  g_observers.Get().SyncNotify(FROM_HERE, &MemoryPressureListener::SyncNotify,
+                               memory_pressure_level);
   g_observers.Get().Notify(FROM_HERE, &MemoryPressureListener::Notify,
                            memory_pressure_level);
 }