Hold reference to stream in CloseAndLockAndDisturb

Some crashes in CloseAndLockAndDisturb may be caused by early collection
of the stream referenced by BodyStreamBuffer. Keep an extra reference to
the stream on the stack as a speculative workaround.

BUG=882599

Change-Id: I798a175cbac6414a7a70cfcb1e924624232a0a19
Reviewed-on: https://chromium-review.googlesource.com/1218123Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590255}

third_party/blink/renderer/core/fetch/body_stream_buffer.cc

@@ -373,6 +373,14 @@ bool BodyStreamBuffer::IsStreamDisturbedForDCheck() {
 }
 
 void BodyStreamBuffer::CloseAndLockAndDisturb(ExceptionState& exception_state) {
+  // Speculative fix for https://crbug.com/882599. Stop the stream from being
+  // garbage collected while this function is executing.
+  // TODO(ricea): Remove this when a better solution is found or if it doesn't
+  // work.
+  v8::Local<v8::Value> stream_handle =
+      stream_.NewLocal(script_state_->GetIsolate());
+  CHECK(!stream_handle.IsEmpty());
+
   base::Optional<bool> is_readable = IsStreamReadable(exception_state);
   if (exception_state.HadException())
     return;