Zero AudioBus internal aligned memory

This prevents from reading uninitialized memory according to MSAN
reports.

Change-Id: Ifccecf69e6df67ab1d2226155a20455ca5c6e293

BUG=856537

Change-Id: Ifccecf69e6df67ab1d2226155a20455ca5c6e293
Reviewed-on: https://chromium-review.googlesource.com/1113935Reviewed-by: Max Morin <maxmorin@chromium.org>
Commit-Queue: Max Morin <maxmorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570367}

media/base/audio_bus.cc

@@ -73,6 +73,7 @@ AudioBus::AudioBus(int channels, int frames)
       size, AudioBus::kChannelAlignment)));
 
   BuildChannelData(channels, aligned_frames, data_.get());
+  Zero();
 }
 
 AudioBus::AudioBus(int channels, int frames, float* data)

media/base/audio_bus_unittest.cc

@@ -133,6 +133,7 @@ TEST_F(AudioBusTest, Create) {
   std::unique_ptr<AudioBus> bus = AudioBus::Create(kChannels, kFrameCount);
   VerifyChannelAndFrameCount(bus.get());
   VerifyReadWriteAndAlignment(bus.get());
+  EXPECT_TRUE(bus->AreFramesZero());
 }
 
 // Verify Create(...) using AudioParameters works as advertised.
@@ -142,6 +143,7 @@ TEST_F(AudioBusTest, CreateUsingAudioParameters) {
                       kSampleRate, kFrameCount));
   VerifyChannelAndFrameCount(bus.get());
   VerifyReadWriteAndAlignment(bus.get());
+  EXPECT_TRUE(bus->AreFramesZero());
 }
 
 // Verify an AudioBus created via CreateWrapper(...) works as advertised.