MC: WIP: dispatching notifications from browser to renderer

components/memory_coordinator/browser/memory_coordinator.h

Index: components/memory_coordinator/browser/memory_coordinator.h
diff --git a/components/memory_coordinator/browser/memory_coordinator.h b/components/memory_coordinator/browser/memory_coordinator.h
index d6871798d3a1a38fbc2824b5b6de7a364fb97337..e4ac37366d1cc836f417d1c9edae1efce0e87488 100644
--- a/components/memory_coordinator/browser/memory_coordinator.h
+++ b/components/memory_coordinator/browser/memory_coordinator.h
@@ -7,6 +7,7 @@
 
 #include "base/memory/memory_pressure_monitor.h"
 #include "components/memory_coordinator/common/client_registry.h"
+#include "components/memory_coordinator/common/memory_coordinator_features.h"
 #include "components/memory_coordinator/public/interfaces/memory_coordinator.mojom.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
@@ -19,17 +20,26 @@ class MemoryCoordinatorHandleImpl;
 // and child processes based on its best knowledge of the memory usage.
 class MemoryCoordinator : public ClientRegistry {
  public:
+  using DispatchCallback = base::MemoryPressureMonitor::DispatchCallback;
+
+  static MemoryCoordinator* GetInstance();
+
   MemoryCoordinator();
   ~MemoryCoordinator() override;
 
   void CreateHandle(int render_process_id,
                     mojom::MemoryCoordinatorHandleRequest request);
 
-  const base::MemoryPressureMonitor::DispatchCallback&
-  pressure_level_dispatcher() {
+  const DispatchCallback& pressure_level_dispatcher() {
     return pressure_level_dispatcher_;
   }
 
+  void SetChildrenDispatchCallback(const DispatchCallback& callback);
+
+  void DispatchToRenderer(
+      int render_process_id,
+      base::MemoryPressureMonitor::MemoryPressureLevel level);
+
   // Returns number of children. Only used for testing.
   size_t NumChildrenForTesting();
 
@@ -39,8 +49,17 @@ class MemoryCoordinator : public ClientRegistry {
   // Called when MemoryPressureMonitor detects memory pressure.
   void OnMemoryPressure(base::MemoryPressureMonitor::MemoryPressureLevel level);
 
+  // Default implementation of |children_dispatch_callback_|. Translates
+  // pressure level to memory state and sends it all renderers synchronously.
+  void DispatchMemoryPressureToChildren(
+      base::MemoryPressureMonitor::MemoryPressureLevel level);
+
   // A callback invoked when MemoryPressureMonitor detects memory pressure.
-  base::MemoryPressureMonitor::DispatchCallback pressure_level_dispatcher_;
+  DispatchCallback pressure_level_dispatcher_;
+
+  // A callback invoked in OnMemoryPressure() to dispatch memory pressure to
+  // child processes.
+  DispatchCallback children_dispatch_callback_;
 
   // Mappings of RenderProcessHost::GetID() -> MemoryCoordinatorHandleImpl.
   // A mapping is added when a renderer connects to MemoryCoordinator and