Re-land: base: Introduce an explicit call for reducing emulated discardable memory usage.

base/memory/discardable_memory_mac.cc

Index: base/memory/discardable_memory_mac.cc
diff --git a/base/memory/discardable_memory_mac.cc b/base/memory/discardable_memory_mac.cc
index b2184e7d589c415f5cd98f09b0e77786d42333a2..8232ecf6eeedee93692b3992a9a0293cd96d776e 100644
--- a/base/memory/discardable_memory_mac.cc
+++ b/base/memory/discardable_memory_mac.cc
@@ -160,16 +160,6 @@ class DiscardableMemoryMac
 }  // namespace
 
 // static
-void DiscardableMemory::RegisterMemoryPressureListeners() {
-  internal::DiscardableMemoryEmulated::RegisterMemoryPressureListeners();
-}
-
-// static
-void DiscardableMemory::UnregisterMemoryPressureListeners() {
-  internal::DiscardableMemoryEmulated::UnregisterMemoryPressureListeners();
-}
-
-// static
 bool DiscardableMemory::ReduceMemoryUsage() {
   return internal::DiscardableMemoryEmulated::ReduceMemoryUsage();
 }