This significantly reduces the amount of overhead incurred when naively importing large external modules without referencing many of its members, which should directly improve response times in the playground. For example, the repro code attached to rdar://problem/16387393 imports Foundation but references none of its members, and with these changes its total compilation time is almost 2.5x faster.
Swift SVN r15479
Take DynamicSelf as a keyword, but parse it as a type-identifier.
Teach function declaration checking to sniff out and validate
DynamicSelf early, with appropriate QoI for references to DynamicSelf
that appear in other places.
As a temporary hack, DynamicSelf resolves to an alias for 'Self' in a
protocol or the enclosing nominal type.
Swift SVN r12708
