Remove callers of mojo::Array<size_t> constructor in favor of ::New

This creates an ambiguity with Array(0) if we try to add a
mojo::Array(std::nullptr_t) constructor. This just removes callers, it
doesn't remove the constructor itself. I'll remove the constructor after
verifying downstream consumers won't be broken.

R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/1397133002 .
diff --git a/services/files/directory_impl.cc b/services/files/directory_impl.cc
index c903a75..79e523a 100644
--- a/services/files/directory_impl.cc
+++ b/services/files/directory_impl.cc
@@ -125,7 +125,7 @@
     return;
   }
 
-  Array<DirectoryEntryPtr> result(0);
+  auto result = Array<DirectoryEntryPtr>::New(0);
 
 // Warning: This is not portable (per POSIX.1 -- |buffer| may not be large
 // enough), but it's fine for Linux.