Revert "[RTCInsertableStreams] Always sync JS ArrayBuffer with internal buffer."

This reverts commit 8b1fecff.

Reason for revert: Causes bot failures. https://crbug.com/1057949

Original change's description:
> [RTCInsertableStreams] Always sync JS ArrayBuffer with internal buffer.
> 
> It is possible to modify the data field without replacing it, so syncing
> always.
> Will work on an optimization for a follow-up CL.
> 
> Bug: 1052765
> Change-Id: Ibc5b143413163f12af3c6cacefb3a9ee028b7eb1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2083092
> Reviewed-by: Harald Alvestrand <hta@chromium.org>
> Commit-Queue: Guido Urdaneta <guidou@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#746093}

TBR=hta@chromium.org,guidou@chromium.org

Change-Id: I69c89db2923f8279fdb40bd7415157dfbb48a189
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1052765
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2082921Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746300}

third_party/blink/renderer/modules/peerconnection/rtc_encoded_video_frame.cc

@@ -46,6 +46,7 @@ DOMArrayBuffer* RTCEncodedVideoFrame::additionalData() const {
 
 void RTCEncodedVideoFrame::setData(DOMArrayBuffer* data) {
   frame_data_ = data;
+  replaced_frame_data_ = true;
 }
 
 String RTCEncodedVideoFrame::toString() const {
@@ -65,12 +66,14 @@ String RTCEncodedVideoFrame::toString() const {
 
 std::unique_ptr<webrtc::video_coding::EncodedFrame>
 RTCEncodedVideoFrame::PassDelegate() {
-  // Sync the delegate data with |frame_data_|.
-  rtc::scoped_refptr<webrtc::EncodedImageBuffer> webrtc_image =
-      webrtc::EncodedImageBuffer::Create(
-          static_cast<const uint8_t*>(frame_data_->Data()),
-          frame_data_->ByteLengthAsSizeT());
-  delegate_->SetEncodedData(std::move(webrtc_image));
+  // Sync the delegate data with |frame_data_| if necessary.
+  if (replaced_frame_data_) {
+    rtc::scoped_refptr<webrtc::EncodedImageBuffer> webrtc_image =
+        webrtc::EncodedImageBuffer::Create(
+            static_cast<const uint8_t*>(frame_data_->Data()),
+            frame_data_->ByteLengthAsSizeT());
+    delegate_->SetEncodedData(std::move(webrtc_image));
+  }
   return std::move(delegate_);
 }
 

third_party/blink/renderer/modules/peerconnection/rtc_encoded_video_frame.h

@@ -52,6 +52,7 @@ class MODULES_EXPORT RTCEncodedVideoFrame final : public ScriptWrappable {
  private:
   std::unique_ptr<webrtc::video_coding::EncodedFrame> delegate_;
   std::vector<uint8_t> additional_data_vector_;
+  bool replaced_frame_data_ = false;
   // Exposes encoded frame data from |delegate_|.
   mutable Member<DOMArrayBuffer> frame_data_;
   // Exposes data from |additional_data_vector_|.