base: Add NOTREACHED() for when using a non-supported discardable memory type.

base/memory/discardable_memory_mac.cc

Index: base/memory/discardable_memory_mac.cc
diff --git a/base/memory/discardable_memory_mac.cc b/base/memory/discardable_memory_mac.cc
index 231eb17153a3a13560aa2239b34a9511be3a5f49..65cae00992c253509bf988626e3640a5a2a0d693 100644
--- a/base/memory/discardable_memory_mac.cc
+++ b/base/memory/discardable_memory_mac.cc
@@ -175,9 +175,6 @@ void DiscardableMemory::GetSupportedTypes(
 scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemoryWithType(
     DiscardableMemoryType type, size_t size) {
   switch (type) {
-    case DISCARDABLE_MEMORY_TYPE_NONE:
-    case DISCARDABLE_MEMORY_TYPE_ASHMEM:
-      return scoped_ptr<DiscardableMemory>();
     case DISCARDABLE_MEMORY_TYPE_MAC: {
       scoped_ptr<DiscardableMemoryMac> memory(new DiscardableMemoryMac(size));
       if (!memory->Initialize())
@@ -201,6 +198,10 @@ scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemoryWithType(
 
       return memory.PassAs<DiscardableMemory>();
     }
+    case DISCARDABLE_MEMORY_TYPE_NONE:
+    case DISCARDABLE_MEMORY_TYPE_ASHMEM:
+      NOTREACHED();
+      return scoped_ptr<DiscardableMemory>();
   }
 
   NOTREACHED();