[MemoryPressureListener] Notify listeners when returning to no pressure

Eventually, the memory pressure listeners will be migrated to the
base::MemoryConsumer API.

A major difference is that the base:MemoryConsumer notifications are
stateful. You only get notifications when transitioning from a state to
another.

Memory pressure notifications for MODERATE and CRITICAL state can be
sent repeatedly, while the NONE state never triggers any notifications.

In order to ease the transition, memory pressure notifications will
be modified to be a stateful API.

The first step is to notify when transitioning to the NONE state.
This is a no-op change as  all current listeners were modified to ensure they ignore those notifications correctly.

Bug: 462288601
Change-Id: I87ad8fffa0914e7f66b5320a745d708b1929b748
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7168577
Commit-Queue: Patrick Monette <[email protected]>
Reviewed-by: Francois Pierre Doray <[email protected]>
Reviewed-by: Thomas Anderson <[email protected]>
Reviewed-by: Vovo Yang <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1550203}
NOKEYCHECK=True
GitOrigin-RevId: d139d7a70867886298ae3826082bb1ebe168746c

Author: plmonette-zz

memory/memory_pressure_listener_registry.cc

@@ -95,6 +95,10 @@ void MemoryPressureListenerRegistry::DoNotifyMemoryPressure(
   CHECK(
       !SingleThreadTaskRunner::HasMainThreadDefault() ||
       SingleThreadTaskRunner::GetMainThreadDefault()->BelongsToCurrentThread());
+  // Don't repeat MEMORY_PRESSURE_LEVEL_NONE notifications.
+  CHECK(memory_pressure_level != base::MEMORY_PRESSURE_LEVEL_NONE ||
+        last_memory_pressure_level_ != memory_pressure_level);
+  last_memory_pressure_level_ = memory_pressure_level;
   if (base::FeatureList::IsEnabled(kSuppressMemoryListeners)) {
     auto mask = kSuppressMemoryListenersMask.Get();
     for (auto& listener : listeners_) {

memory/memory_pressure_listener_registry.h

@@ -49,6 +49,9 @@ class BASE_EXPORT MemoryPressureListenerRegistry {
  private:
   void DoNotifyMemoryPressure(MemoryPressureLevel memory_pressure_level);
 
+  base::MemoryPressureLevel last_memory_pressure_level_ =
+      base::MEMORY_PRESSURE_LEVEL_NONE;
+
   base::ObserverList<SyncMemoryPressureListenerRegistration>::Unchecked
       listeners_;
 };