Revert of base: Introduce an explicit call for reducing emulated discardable memory usage.

base/memory/discardable_memory_emulated.cc

Index: base/memory/discardable_memory_emulated.cc
diff --git a/base/memory/discardable_memory_emulated.cc b/base/memory/discardable_memory_emulated.cc
index f9097b186e1405897f2a85c17f52398f0e90a1ac..340a181834ad3dbed5058cd419467f05013bc6f8 100644
--- a/base/memory/discardable_memory_emulated.cc
+++ b/base/memory/discardable_memory_emulated.cc
@@ -13,12 +13,14 @@
 // This is admittedly pretty magical.
 const size_t kEmulatedMemoryLimit = 512 * 1024 * 1024;
 const size_t kEmulatedSoftMemoryLimit = 32 * 1024 * 1024;
+const size_t kEmulatedBytesToKeepUnderModeratePressure = 4 * 1024 * 1024;
 const size_t kEmulatedHardMemoryLimitExpirationTimeMs = 1000;
 
 struct SharedState {
   SharedState()
       : manager(kEmulatedMemoryLimit,
                 kEmulatedSoftMemoryLimit,
+                kEmulatedBytesToKeepUnderModeratePressure,
                 TimeDelta::FromMilliseconds(
                     kEmulatedHardMemoryLimitExpirationTimeMs)) {}
 
@@ -43,14 +45,18 @@
 }
 
 // static
-bool DiscardableMemoryEmulated::ReduceMemoryUsage() {
-  return g_shared_state.Pointer()->manager.ReduceMemoryUsage();
+void DiscardableMemoryEmulated::RegisterMemoryPressureListeners() {
+  g_shared_state.Pointer()->manager.RegisterMemoryPressureListener();
 }
 
 // static
-void DiscardableMemoryEmulated::ReduceMemoryUsageUntilWithinLimit(
-    size_t bytes) {
-  g_shared_state.Pointer()->manager.ReduceMemoryUsageUntilWithinLimit(bytes);
+void DiscardableMemoryEmulated::UnregisterMemoryPressureListeners() {
+  g_shared_state.Pointer()->manager.UnregisterMemoryPressureListener();
+}
+
+// static
+bool DiscardableMemoryEmulated::ReduceMemoryUsage() {
+  return g_shared_state.Pointer()->manager.ReduceMemoryUsage();
 }
 
 // static