Enable oilpan for WebMIDI by default

Systematic change:
- XWillBeY -> Y
- XWillBeNoop(Z) -> Z

BUG=340522

Review URL: https://codereview.chromium.org/354573002

git-svn-id: svn://svn.chromium.org/blink/trunk@176919 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL: Generate all constructor callbacks with the same template macro

Regular constructors and named constructors are similar enough that using
separate template macros to generate them mostly leads to duplicated code.

The actual difference is now more visible, since it takes the explicit
form

  {% if constructor.is_named_constructor %}
  // the difference
  {% endif %}

in the shared macro.

Review URL: https://codereview.chromium.org/349523004

git-svn-id: svn://svn.chromium.org/blink/trunk@176920 bbb929c8-8fbe-4397-9dbb-9b2b20218538