Extending supported sample rate from 3.0KHz to 192.0KHz for OfflineAudioContext.

Currently, AudioBuffer is supported 3.0KHz to 192.0 KHz.
However, offlineAudioContext is not supported lower sample rate than 44.0KHz.

http://webaudio.github.io/web-audio-api/#the-audiobuffersourcenode-interface

“Describes the sample-rate of the linear PCM audio data
in the buffer in sample-frames per second.
An implementation must support sample-rates
in at least the range 22050 to 96000”

Changed supported sampleRate range 3KHz to 192KHz and fftsize for convolution.

BUG=394009

Review URL: https://codereview.chromium.org/375383002

git-svn-id: svn://svn.chromium.org/blink/trunk@181816 bbb929c8-8fbe-4397-9dbb-9b2b20218538