[wasm] Add a flag to enable/disable async compile.

src/wasm/wasm-module.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <memory>
 
 #include "src/assembler-inl.h"
 #include "src/base/adapters.h"
 #include "src/base/atomic-utils.h"
 #include "src/code-stubs.h"
@@ skipping 3020 matching lines @@
         // If no more work, then this job is done. Predictable mode is handled
         // specially though, see above.
         if (!FLAG_verify_predictable) delete job_;
       }
     }
   };
 };
 
 void wasm::AsyncCompile(Isolate* isolate, Handle<JSPromise> promise,
                         const ModuleWireBytes& bytes) {
+  if (!FLAG_wasm_async_compilation) {
+    ErrorThrower thrower(isolate, "WasmCompile");
+    // Compile the module.
+    MaybeHandle<WasmModuleObject> module_object =
+        SyncCompile(isolate, &thrower, bytes);
+    if (thrower.error()) {
+      RejectPromise(isolate, handle(isolate->context()), &thrower, promise);
+      return;
+    }
+    Handle<WasmModuleObject> module = module_object.ToHandleChecked();
+    ResolvePromise(isolate, handle(isolate->context()), promise, module);
+    return;
+  }
+
   // Make a copy of the wire bytes in case the user program changes them
   // during asynchronous compilation.
   std::unique_ptr<byte[]> copy(new byte[bytes.length()]);
   memcpy(copy.get(), bytes.start(), bytes.length());
   auto job = new AsyncCompileJob(isolate, std::move(copy), bytes.length(),
                                  handle(isolate->context()), promise);
   job->Start();
   // Special handling for predictable mode, see above.
   if (FLAG_verify_predictable) delete job;
 }
@@ skipping 255 matching lines @@
                                      callee_compiled->instruction_start());
     }
     DCHECK_EQ(non_compiled_functions.size(), idx);
   }
 
   Code* ret =
       Code::cast(compiled_module->code_table()->get(func_to_return_idx));
   DCHECK_EQ(Code::WASM_FUNCTION, ret->kind());
   return handle(ret, isolate);
 }