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

base/memory/discardable_memory_manager_unittest.cc

Index: base/memory/discardable_memory_manager_unittest.cc
diff --git a/base/memory/discardable_memory_manager_unittest.cc b/base/memory/discardable_memory_manager_unittest.cc
index ef5739a6526a5e03495d82c3b136c44f2b162e99..5cf8391197d1401055c58390644d9b0b2bead3aa 100644
--- a/base/memory/discardable_memory_manager_unittest.cc
+++ b/base/memory/discardable_memory_manager_unittest.cc
@@ -5,7 +5,6 @@
 #include "base/memory/discardable_memory_manager.h"
 
 #include "base/bind.h"
-#include "base/run_loop.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -68,9 +67,7 @@ class TestDiscardableMemoryManagerImpl
 
 class DiscardableMemoryManagerTestBase {
  public:
-  DiscardableMemoryManagerTestBase() {
-    manager_.RegisterMemoryPressureListener();
-  }
+  DiscardableMemoryManagerTestBase() {}
 
  protected:
   enum LockStatus {
@@ -127,10 +124,15 @@ class DiscardableMemoryManagerTestBase {
 
   void SetNow(TimeTicks now) { manager_.SetNow(now); }
 
+  void PurgeAll() { return manager_.PurgeAll(); }
+
   bool ReduceMemoryUsage() { return manager_.ReduceMemoryUsage(); }
 
+  void ReduceMemoryUsageUntilWithinModeratePressureLimit() {
+    manager_.ReduceMemoryUsageUntilWithinModeratePressureLimit();
+  }
+
  private:
-  MessageLoopForIO message_loop_;
   TestDiscardableMemoryManagerImpl manager_;
 };
 
@@ -192,11 +194,7 @@ TEST_F(DiscardableMemoryManagerTest, LockAfterPurge) {
   EXPECT_TRUE(CanBePurged(&allocation));
 
   // Force the system to purge.
-  MemoryPressureListener::NotifyMemoryPressure(
-      MemoryPressureListener::MEMORY_PRESSURE_CRITICAL);
-
-  // Required because ObserverListThreadSafe notifies via PostTask.
-  RunLoop().RunUntilIdle();
+  PurgeAll();
 
   EXPECT_EQ(LOCK_STATUS_PURGED, Lock(&allocation));
   EXPECT_FALSE(CanBePurged(&allocation));
@@ -301,17 +299,15 @@ class DiscardableMemoryManagerPermutationTest
   TestAllocationImpl allocation_[3];
 };
 
-// Verify that memory was discarded in the correct order after applying
-// memory pressure.
+// Verify that memory was discarded in the correct order after reducing usage to
+// moderate pressure limit.
 TEST_P(DiscardableMemoryManagerPermutationTest, LRUDiscardedModeratePressure) {
   RegisterAndUseAllocations();
 
   SetBytesToKeepUnderModeratePressure(1024);
   SetMemoryLimit(2048);
 
-  MemoryPressureListener::NotifyMemoryPressure(
-      MemoryPressureListener::MEMORY_PRESSURE_MODERATE);
-  RunLoop().RunUntilIdle();
+  ReduceMemoryUsageUntilWithinModeratePressureLimit();
 
   EXPECT_NE(LOCK_STATUS_FAILED, Lock(allocation(2)));
   EXPECT_EQ(LOCK_STATUS_PURGED, Lock(allocation(1)));
@@ -358,9 +354,7 @@ TEST_P(DiscardableMemoryManagerPermutationTest, LRUDiscardedAmount) {
 TEST_P(DiscardableMemoryManagerPermutationTest, PurgeFreesAllUnlocked) {
   RegisterAndUseAllocations();
 
-  MemoryPressureListener::NotifyMemoryPressure(
-      MemoryPressureListener::MEMORY_PRESSURE_CRITICAL);
-  RunLoop().RunUntilIdle();
+  PurgeAll();
 
   for (int i = 0; i < 3; ++i) {
     if (i == 0)