[wasm] Deliver streaming client callback in background

If streaming compilation has been triggered on a worker, it can be
problematic to schedule a foreground task for the callback, since
workers might never return to the event queue. Hence, deliver the
callback in background. This is possible after this blink-side change:
https://crrev.com/c/1901592

R=ahaas@chromium.org
CC=​bbudge@chromium.org

Bug: chromium:1018029
Cq-Include-Trybots: luci.v8.try:v8_linux_blink_rel
Change-Id: I568c39cf97e94f6d1cec01090ece81e4521fa47c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1914199Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64946}

src/wasm/wasm-js.cc

@@ -70,20 +70,9 @@ class WasmStreaming::WasmStreamingImpl {
   }
 
   void SetClient(std::shared_ptr<Client> client) {
-    // There are no other event notifications so just pass client to decoder.
-    // Wrap the client with a callback to trigger the callback in a new
-    // foreground task.
-    i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate_);
-    v8::Platform* platform = i::V8::GetCurrentPlatform();
-    std::shared_ptr<TaskRunner> foreground_task_runner =
-        platform->GetForegroundTaskRunner(isolate_);
     streaming_decoder_->SetModuleCompiledCallback(
-        [client, i_isolate, foreground_task_runner](
-            const std::shared_ptr<i::wasm::NativeModule>& native_module) {
-          foreground_task_runner->PostTask(
-              i::MakeCancelableTask(i_isolate, [client, native_module] {
-                client->OnModuleCompiled(Utils::Convert(native_module));
-              }));
+        [client](const std::shared_ptr<i::wasm::NativeModule>& native_module) {
+          client->OnModuleCompiled(Utils::Convert(native_module));
         });
   }