Remove unneeded const casts from AudioBus and FFTFrame

This also improves const correctness of FFTFrame.

Bug: 822721
Change-Id: I49668b37b0ecca278ce35af293eee6e324d88f4c
Reviewed-on: https://chromium-review.googlesource.com/962223Reviewed-by: Raymond Toy <rtoy@chromium.org>
Commit-Queue: Eero Häkkinen <eero.hakkinen@intel.com>
Cr-Commit-Position: refs/heads/master@{#544053}

third_party/WebKit/Source/modules/webaudio/RealtimeAnalyser.cpp

@@ -161,7 +161,7 @@ void RealtimeAnalyser::DoFFTAnalysis() {
   // Do the analysis.
   analysis_frame_->DoFFT(temp_p);
 
-  float* real_p = analysis_frame_->RealData();
+  const float* real_p = analysis_frame_->RealData();
   float* imag_p = analysis_frame_->ImagData();
 
   // Blow away the packed nyquist component.

third_party/WebKit/Source/platform/audio/AudioBus.cpp

@@ -500,12 +500,11 @@ void AudioBus::CopyWithGainFrom(const AudioBus& source_bus, float gain) {
   if (this == &source_bus && gain == 1)
     return;
 
-  AudioBus& source_bus_safe = const_cast<AudioBus&>(source_bus);
   const float* sources[kMaxBusChannels];
   float* destinations[kMaxBusChannels];
 
   for (unsigned i = 0; i < number_of_channels; ++i) {
-    sources[i] = source_bus_safe.Channel(i)->Data();
+    sources[i] = source_bus.Channel(i)->Data();
     destinations[i] = Channel(i)->MutableData();
   }
 

third_party/WebKit/Source/platform/audio/AudioBus.h

@@ -81,7 +81,7 @@ class PLATFORM_EXPORT AudioBus : public ThreadSafeRefCounted<AudioBus> {
 
   AudioChannel* Channel(unsigned channel) { return channels_[channel].get(); }
   const AudioChannel* Channel(unsigned channel) const {
-    return const_cast<AudioBus*>(this)->channels_[channel].get();
+    return channels_[channel].get();
   }
   AudioChannel* ChannelByType(unsigned type);
   const AudioChannel* ChannelByType(unsigned type) const;

third_party/WebKit/Source/platform/audio/FFTConvolver.cpp

@@ -40,7 +40,7 @@ FFTConvolver::FFTConvolver(size_t fft_size)
       output_buffer_(fft_size),
       last_overlap_buffer_(fft_size / 2) {}
 
-void FFTConvolver::Process(FFTFrame* fft_kernel,
+void FFTConvolver::Process(const FFTFrame* fft_kernel,
                            const float* source_p,
                            float* dest_p,
                            size_t frames_to_process) {

third_party/WebKit/Source/platform/audio/FFTConvolver.h

@@ -53,7 +53,7 @@ class PLATFORM_EXPORT FFTConvolver {
   // The input to output latency is equal to fftSize / 2
   //
   // Processing in-place is allowed...
-  void Process(FFTFrame* fft_kernel,
+  void Process(const FFTFrame* fft_kernel,
                const float* source_p,
                float* dest_p,
                size_t frames_to_process);

third_party/WebKit/Source/platform/audio/FFTFrame.cpp

@@ -251,7 +251,7 @@ void FFTFrame::AddConstantGroupDelay(double sample_frame_delay) {
 
 void FFTFrame::Multiply(const FFTFrame& frame) {
   FFTFrame& frame1 = *this;
-  FFTFrame& frame2 = const_cast<FFTFrame&>(frame);
+  const FFTFrame& frame2 = frame;
 
   float* real_p1 = frame1.RealData();
   float* imag_p1 = frame1.ImagData();

third_party/WebKit/Source/platform/audio/FFTFrame.h

@@ -70,8 +70,10 @@ class PLATFORM_EXPORT FFTFrame {
   void DoFFT(const float* data);
   void DoInverseFFT(float* data);
 
-  float* RealData() const { return const_cast<float*>(real_data_.Data()); }
-  float* ImagData() const { return const_cast<float*>(imag_data_.Data()); }
+  float* RealData() { return real_data_.Data(); }
+  const float* RealData() const { return real_data_.Data(); }
+  float* ImagData() { return imag_data_.Data(); }
+  const float* ImagData() const { return imag_data_.Data(); }
 
   unsigned FftSize() const { return fft_size_; }
   unsigned Log2FFTSize() const { return log2fft_size_; }

third_party/WebKit/Source/platform/audio/ffmpeg/FFTFrameFFMPEG.cpp

@@ -143,7 +143,7 @@ float* FFTFrame::GetUpToDateComplexData() {
     c[base_complex_index] = real[i];
     c[base_complex_index + 1] = imag[i];
   }
-  return const_cast<float*>(complex_data_.Data());
+  return c;
 }
 
 RDFTContext* FFTFrame::ContextForSize(unsigned fft_size, int trans) {