Replace memcopy with memmove for overlapping copies

copyFromChannel can produce overlapping areas when the source array is
the same as the channel data array.  Use memmove instead of memcpy to
handle this case.  copyToChannel has the same issue, so fix that too.

Manually tested the repro case with a local asan build.  The issue no
longer reproduces.

Bug: 1081722
Change-Id: I168ef418fccf45646bb4d8a01c22cecfbd5da20b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2202394Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769034}

third_party/blink/renderer/modules/webaudio/audio_buffer.cc

@@ -254,7 +254,7 @@ void AudioBuffer::copyFromChannel(NotShared<DOMFloat32Array> destination,
   DCHECK_LE(count, data_length);
   DCHECK_LE(buffer_offset + count, data_length);
 
-  memcpy(dst, src + buffer_offset, count * sizeof(*src));
+  memmove(dst, src + buffer_offset, count * sizeof(*src));
 }
 
 void AudioBuffer::copyToChannel(NotShared<DOMFloat32Array> source,
@@ -297,7 +297,7 @@ void AudioBuffer::copyToChannel(NotShared<DOMFloat32Array> source,
   DCHECK_LE(buffer_offset + count, channel_data->lengthAsSizeT());
   DCHECK_LE(count, source.View()->lengthAsSizeT());
 
-  memcpy(dst + buffer_offset, src, count * sizeof(*dst));
+  memmove(dst + buffer_offset, src, count * sizeof(*dst));
 }
 
 void AudioBuffer::Zero() {