Web Animations CSS: Fix and clean up compositableValuesFor* methods

The compositableValuesForAnimations and compositableValuesForTransitions
methods were accidentally implemented switched, so that each returns the
CompositableValueMap that the other should have returned. This basically
means that they end up being applied in the wrong order in the cascade.

This patch fixes this behaviour, and adds a test checking animations are
applied before !important. We'll add a similar test for transitions once
the virtual test suite for transitions/web-animations-css is enabled.

We also make some minor clean-ups to simplify the code, passing pointers
to AnimationStack::compositableValues, instead of references and values.
In the normal case, we won't have an update and these will just be null.

BUG=303430, 232273

Review URL: https://codereview.chromium.org/39503002

git-svn-id: svn://svn.chromium.org/blink/trunk@160702 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Get rid of AbstractView.idl

This CL removes 'AbstractView.idl' as it is unused.

Review URL: https://codereview.chromium.org/48153002

git-svn-id: svn://svn.chromium.org/blink/trunk@160703 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Allow comments inside IDL interface extended attributes

Comments inside IDL extended attributes don't work, due to ad hoc parsing
in compute_dependencies.py failing to parse these correctly, thus not
generated constructor on global objects IDL files correctly.

This fixes this by explicitly stripping comments,
and also has some minor cleanup.

No change in generated code.

Also noticed two other bugs, to fix in followups.

BUG=311575

Review URL: https://codereview.chromium.org/47943002

git-svn-id: svn://svn.chromium.org/blink/trunk@160704 bbb929c8-8fbe-4397-9dbb-9b2b20218538