base: Use DiscardableMemoryManager on MacOSX.

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 c59d82e51695ef8531626faa8d1934cad74a62f0..8b08cf62c48f13cefff73a97b9729089617919ec 100644
--- a/base/memory/discardable_memory_manager_unittest.cc
+++ b/base/memory/discardable_memory_manager_unittest.cc
@@ -42,9 +42,16 @@ class TestAllocationImpl : public internal::DiscardableMemoryManagerAllocation {
   bool is_locked_;
 };
 
+// Tests can assume that the default limit is at least 1024. Tests that rely on
+// something else needs to explicit set the limit.
+const size_t kDefaultMemoryLimit = 1024;
+const size_t kDefaultBytesToKeepUnderModeratePressure = kDefaultMemoryLimit;
+
 class DiscardableMemoryManagerTestBase {
  public:
-  DiscardableMemoryManagerTestBase() {
+  DiscardableMemoryManagerTestBase()
+      : manager_(kDefaultMemoryLimit,
+                 kDefaultBytesToKeepUnderModeratePressure) {
     manager_.RegisterMemoryPressureListener();
   }