Add Web Audio API to Webkit

The Web Audio API introduces a variety of new audio features to the web platform. It can be used with the canvas 2D and WebGL 3D graphics APIs for creating a new generation of games and interactive applications. The API is capable of dynamically positioning/spatializing and mixing multiple sound sources in three-dimensional space. It has a powerful modular routing system, supporting effects, a convolution engine for room simulation, multiple sends, submixes, etc. Scheduled sound playback is provided for musical applications requiring a high degree of rhythmic precision. Realtime analysis / visualizer support and direct JavaScript processing is also supported.