Add Perl IDL support for method parameter type sequence<Dictionary>

This patch adds support to the Perl IDL generator for sequence<Dictionary>
parameters on IDL methods.
This introduces a DictionarySequence class to wrap the JS array-like
object instead of using a Vector<Dictionary> because Dictionaries cannot
be heap allocated.

BUG=257235

Review URL: https://codereview.chromium.org/74533003

git-svn-id: svn://svn.chromium.org/blink/trunk@162335 bbb929c8-8fbe-4397-9dbb-9b2b20218538