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 8c1aee896887aa95ec78e9035fc975c9fab93a73..84dfbc6df8adbddacc8d9f8cc5d1a887b0cb0e03 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();