Simplified discreteTimeConstantForSampleRate

Simplified discreteTimeConstantForSampleRate
https://bugs.webkit.org/show_bug.cgi?id=78051

Remove hardcoded constant and simplify computation of discrete
time constant.

Patch by Raymond Toy <rtoy@google.com> on 2012-03-03
Reviewed by Chris Rogers.

No new tests needed.  Covered by existing AudioParam tests.

* platform/audio/AudioUtilities.cpp:
(WebCore::AudioUtilities::discreteTimeConstantForSampleRate):
Simplify formula.
* platform/audio/AudioUtilities.h:
(AudioUtilities): Update function signature.
* platform/audio/DynamicsCompressorKernel.cpp:
(WebCore::DynamicsCompressorKernel::DynamicsCompressorKernel):
cast to float to avoid warnings.
* webaudio/AudioParamTimeline.cpp:
(WebCore::AudioParamTimeline::valuesForTimeRangeImpl): cast to
float to avoid warnings.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@109665 268f45cc-cd09-0410-ab3c-d52691b4dbfc