Add HitRegionOptions IDL dictionary

To replace generic Dictionary. Renamed existing HitRegionOptions
struct to HitRegionOptionsInternal to resolve name conflict.
The spec[1] doesn't contain |path| and |fillRule| members, but
this CL added them because the current implementation uses them.
This CL also removed unused addHitRegion() which doesn't take
HitRegionOptions.

Tests under fast/canvas cover this change.

[1] http://www.w3.org/TR/2dcontext/#hitregionoptions

BUG=403150

Review URL: https://codereview.chromium.org/569483004

git-svn-id: svn://svn.chromium.org/blink/trunk@182138 bbb929c8-8fbe-4397-9dbb-9b2b20218538