Reduce Remove dynamic memory allocations in AudioSourceProviderImpl

Reduce the frequency of dynamic memory allocations
in MediaStreamComponent::AudioSourceProviderImpl::ProvideInput()
which is running a on realtime audio thread.

Bug: 1138927
Change-Id: I73853fd5dcd7e0ab4de42204e81c081d260a3413
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485164
Commit-Queue: Olga Sharonova <olka@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Auto-Submit: Olga Sharonova <olka@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818886}

third_party/blink/renderer/platform/mediastream/media_stream_component.cc

@@ -124,11 +124,13 @@ void MediaStreamComponent::AudioSourceProviderImpl::ProvideInput(
 
   // Wrap the AudioBus channel data using WebVector.
   uint32_t n = bus->NumberOfChannels();
-  WebVector<float*> web_audio_data(n);
+  if (web_audio_data_.size() != n)
+    web_audio_data_ = WebVector<float*>(static_cast<size_t>(n));
+
   for (uint32_t i = 0; i < n; ++i)
-    web_audio_data[i] = bus->Channel(i)->MutableData();
+    web_audio_data_[i] = bus->Channel(i)->MutableData();
 
-  web_audio_source_provider_->ProvideInput(web_audio_data, frames_to_process);
+  web_audio_source_provider_->ProvideInput(web_audio_data_, frames_to_process);
 }
 
 void MediaStreamComponent::Trace(Visitor* visitor) const {

third_party/blink/renderer/platform/mediastream/media_stream_component.h

@@ -35,6 +35,7 @@
 #include <memory>
 
 #include "third_party/blink/public/platform/modules/mediastream/web_media_stream_track.h"
+#include "third_party/blink/public/platform/web_vector.h"
 #include "third_party/blink/renderer/platform/audio/audio_source_provider.h"
 #include "third_party/blink/renderer/platform/heap/handle.h"
 #include "third_party/blink/renderer/platform/mediastream/media_constraints.h"
@@ -125,6 +126,9 @@ class PLATFORM_EXPORT MediaStreamComponent final
    private:
     WebAudioSourceProvider* web_audio_source_provider_;
     Mutex provide_input_lock_;
+
+    // Used to wrap AudioBus to be passed into |web_audio_source_provider_|.
+    WebVector<float*> web_audio_data_;
   };
 
   AudioSourceProviderImpl source_provider_;