Update AudioBufferSourceNode declarations to match current WebAudio spec.

The current WebAudio spec is:

https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=43608506
Fix CheckRequiresForConstructors to recognize fields that are constructor references as constructors so that it doesn't complain that it isn't goog.require'd.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=43780560