Use wrapper_configuration consistently in bindings

Use wrapper_configuration consistently in bindings

Currently the bindings overuse WrapperConfiguration::Dependent.
This changes it to use WrapperConfiguration::Independent
unless Dependent is actually needed, by computing it once
in the interface context.
(Fixes one FIXME and removes some hard-coding.)

This is split off as 1/2 bindings-only change from:
Implement ImageData constructors.
https://codereview.chromium.org/196343032/

BUG=345503
TBR=haraken

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169827

[Nils Barth (inactive), 2014-03-24 03:06:39]

Split off first bindings-only change;
should be ok, but PTAL.

[Nils Barth (inactive), 2014-03-24 03:06:43]

The CQ bit was checked by nbarth@chromium.org

[commit-bot: I haz the power, 2014-03-24 03:06:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/nbarth@chromium.org/199633014/20001

[haraken, 2014-03-24 03:30:19]

LGTM

[commit-bot: I haz the power, 2014-03-24 06:56:27]

Change committed as 169827