[GStreamer] FFTFrame implementation

[GStreamer] FFTFrame implementation
https://bugs.webkit.org/show_bug.cgi?id=73545

Reviewed by Chris Rogers.

.:

* configure.ac: Enable the WebAudio option again and remove
libfftw checks.

Source/WebCore:

FFTFrame implementation based on GStreamer's FFT processing
library.

No new tests, existing WebAudio tests cover this.

* GNUmakefile.am:
* GNUmakefile.list.am:
* platform/audio/FFTFrame.h:
* platform/audio/FFTFrameStub.cpp:
* platform/audio/gstreamer/FFTFrameGStreamer.cpp: Added.
(WebCore::FFTFrame::FFTFrame):
(WebCore::FFTFrame::initialize):
(WebCore::FFTFrame::cleanup):
(WebCore::FFTFrame::~FFTFrame):
(WebCore::FFTFrame::multiply):
(WebCore::FFTFrame::doFFT):
(WebCore::FFTFrame::doInverseFFT):
(WebCore::FFTFrame::realData):
(WebCore::FFTFrame::imagData):

Source/WebKit/gtk:

* GNUmakefile.am: Remove libfftw compilation flags.

Source/WebKit2:

* GNUmakefile.am: Remove libfftw compilation flags.

LayoutTests:

* webaudio/resources/convolution-testing.js:
(checkTail1): Adapt convolution threshold for GStreamerFFTFrame
implementation, as advised by Chris Rogers.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106537 268f45cc-cd09-0410-ab3c-d52691b4dbfc