Mojo: NULL -> nullptr in mojo/system and mojo/embedder.

mojo/embedder/simple_platform_shared_buffer.cc

Index: mojo/embedder/simple_platform_shared_buffer.cc
diff --git a/mojo/embedder/simple_platform_shared_buffer.cc b/mojo/embedder/simple_platform_shared_buffer.cc
index 278de00069f219c39e93fabbd09a7515936b9446..fc5ee8c7120beac1fcbd41cb7a9375b8c394fc68 100644
--- a/mojo/embedder/simple_platform_shared_buffer.cc
+++ b/mojo/embedder/simple_platform_shared_buffer.cc
@@ -20,7 +20,7 @@ SimplePlatformSharedBuffer* SimplePlatformSharedBuffer::Create(
     // We can't just delete it directly, due to the "in destructor" (debug)
     // check.
     scoped_refptr<SimplePlatformSharedBuffer> deleter(rv);
-    return NULL;
+    return nullptr;
   }
 
   return rv;
@@ -38,7 +38,7 @@ SimplePlatformSharedBuffer::CreateFromPlatformHandle(
     // We can't just delete it directly, due to the "in destructor" (debug)
     // check.
     scoped_refptr<SimplePlatformSharedBuffer> deleter(rv);
-    return NULL;
+    return nullptr;
   }
 
   return rv;