Bug 865253 - Part 1: Implement the DOM bindings for OscillatorNode; r=roc
Bug 865253 - Part 2: Implement the alternate enum values for OscillatorNode; r=roc
Bug 865253 - Part 3: Direct generation of fixed oscillator types. r=ehsan

Simple direct calculation of the fixed types.

We probably want to use the PeriodicWave machinery to generate
the pre-defined waveforms once it's available. In either case
we can optimize this significantly by caching the generated
waveform when the frequency is stationary over the block.
Bug 865253 - Part 4: Stop OscillatorNodes on context shutdown. r=ehsan

Like AudioBufferSourceNode and ScriptProcessorNode, OscillatorNode
holds a self-reference in mPlaying. Keep track of all osc nodes
in the AudioContext and explicitly stop them to make sure this
reference is dropped.
Bug 865253 - Part 5: Shorten a comment to fit in 80 columns. r=ehsan