Support short-hand object literals {foo, bar} everywhere.

This is specified in §12.2.5 of the draft spec (http://people.mozilla.org/~jorendorff/es6-draft.html#sec-object-initializer) by the production [PropertyDefinition : IdentifierReference], and discussed e.g. in http://ariya.ofilabs.com/2013/02/es6-and-object-literal-property-value-shorthand.html.
Add ES6 class externs

These are delineated in §18.3 of the draft spec, Constructor Properties of the Global Object: http://people.mozilla.org/~jorendorff/es6-draft.html#sec-constructor-properties-of-the-global-object.
Support method definitions in object literals.

This is specified in §14.3 of the current draft spec http://people.mozilla.org/~jorendorff/es6-draft.html#sec-method-definitions, and discussed with examples at http://ariya.ofilabs.com/2013/03/es6-and-method-definitions.html.
Add support for 'u' and 'y' RegExp flags in ES6 mode.

These flags are defined in §12.2.7.1 of the draft spec: http://people.mozilla.org/\~jorendorff/es6-draft.html\#sec-primary-expression-regular-expression-literals-static-semantics-early-errors (narrowing the RegularExpressionFlags production defined in §11.8.5).  The new flags are described at https://mathiasbynens.be/notes/es6-unicode-regex.
Support ES6 computed property names.

This is specified by the ComputedPropertyName production in §12.2.5 of the draft ES6 spec: http://people.mozilla.org/~jorendorff/es6-draft.html#sec-object-initializer, and discussed at https://github.com/lukehoban/es6features\#enhanced-object-literals.