base: Use nullptr instead of NULL and static_cast in discardable memory unit tests.

base/memory/discardable_memory_unittest.cc

Index: base/memory/discardable_memory_unittest.cc
diff --git a/base/memory/discardable_memory_unittest.cc b/base/memory/discardable_memory_unittest.cc
index a111cfcc07916a7237fdd7d0b67d55aef1c4f688..2bdc0795d18ba87ef701b74d87db05fd3716275c 100644
--- a/base/memory/discardable_memory_unittest.cc
+++ b/base/memory/discardable_memory_unittest.cc
@@ -65,13 +65,13 @@ TEST_P(DiscardableMemoryTest, LockAndUnLock) {
   const scoped_ptr<DiscardableMemory> memory(CreateLockedMemory(kSize));
   ASSERT_TRUE(memory);
   void* addr = memory->Memory();
-  ASSERT_NE(static_cast<void*>(NULL), addr);
+  ASSERT_NE(nullptr, addr);
 
   memory->Unlock();
 
   EXPECT_NE(DISCARDABLE_MEMORY_LOCK_STATUS_FAILED, memory->Lock());
   addr = memory->Memory();
-  ASSERT_NE(static_cast<void*>(NULL), addr);
+  ASSERT_NE(nullptr, addr);
 
   memory->Unlock();
 }