base: Add soft memory limit to DiscardableMemoryManager.

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 140fdb01e28952acd80025c5bda9591fa67276c3..d1bebc4ab16355e33c35af4de13baa93929740fe 100644
--- a/base/memory/discardable_memory_emulated.cc
+++ b/base/memory/discardable_memory_emulated.cc
@@ -19,7 +19,9 @@ const size_t kEmulatedBytesToKeepUnderModeratePressure =
 struct SharedState {
   SharedState()
       : manager(kEmulatedMemoryLimit,
-                kEmulatedBytesToKeepUnderModeratePressure) {}
+                kEmulatedMemoryLimit,
+                kEmulatedBytesToKeepUnderModeratePressure,
+                TimeDelta::Max()) {}
 
   internal::DiscardableMemoryManager manager;
 };
@@ -52,6 +54,11 @@ void DiscardableMemoryEmulated::UnregisterMemoryPressureListeners() {
 }
 
 // static
+bool DiscardableMemoryEmulated::ReduceMemoryUsage() {
+  return g_shared_state.Pointer()->manager.ReduceMemoryUsage();
+}
+
+// static
 void DiscardableMemoryEmulated::PurgeForTesting() {
   g_shared_state.Pointer()->manager.PurgeAll();
 }