base: Avoid purging more discardable memory than necessary.

base/memory/discardable_memory_provider_unittest.cc

Index: base/memory/discardable_memory_provider_unittest.cc
diff --git a/base/memory/discardable_memory_provider_unittest.cc b/base/memory/discardable_memory_provider_unittest.cc
index f033a0524e727ab1d314b50b31faca888123901c..a1294fbcde9e3034b16065f703d748a923b212ff 100644
--- a/base/memory/discardable_memory_provider_unittest.cc
+++ b/base/memory/discardable_memory_provider_unittest.cc
@@ -232,6 +232,22 @@ TEST_P(DiscardableMemoryProviderPermutationTest, LRUDiscardedExceedLimit) {
   EXPECT_NE(static_cast<void*>(NULL), Memory(discardable(0)));
 }
 
+// Verify that no more memory than necessary was discarded after changing
+// memory limit.
+TEST_P(DiscardableMemoryProviderPermutationTest, LRUDiscardedAmount) {
+  SetBytesToReclaimUnderModeratePressure(2048);
+  SetDiscardableMemoryLimit(4096);
+
+  CreateAndUseDiscardableMemory();
+
+  SetDiscardableMemoryLimit(2048);
+
+  EXPECT_EQ(DISCARDABLE_MEMORY_SUCCESS, discardable(2)->Lock());
+  EXPECT_EQ(DISCARDABLE_MEMORY_PURGED, discardable(1)->Lock());
+  // 0 should still be locked.
+  EXPECT_NE(static_cast<void*>(NULL), Memory(discardable(0)));
+}
+
 TEST_P(DiscardableMemoryProviderPermutationTest,
        CriticalPressureFreesAllUnlocked) {
   CreateAndUseDiscardableMemory();