[wasm] Always make a copy of the wire bytes for a synchronous compile.

R=ahaas@chromium.org,mtrofin@chromium.org

Bug: chromium:759624
Change-Id: I032755698c4f404cfd5bf3298df57a4bcfbe6f2c
Reviewed-on: https://chromium-review.googlesource.com/638590Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47652}

src/wasm/wasm-module.cc

@@ -812,8 +812,13 @@ MaybeHandle<WasmModuleObject> wasm::SyncCompile(Isolate* isolate,
     return {};
   }
 
-  ModuleResult result = SyncDecodeWasmModule(isolate, bytes.start(),
-                                             bytes.end(), false, kWasmOrigin);
+  // TODO(titzer): only make a copy of the bytes if SharedArrayBuffer
+  std::unique_ptr<byte[]> copy(new byte[bytes.length()]);
+  memcpy(copy.get(), bytes.start(), bytes.length());
+  ModuleWireBytes bytes_copy(copy.get(), copy.get() + bytes.length());
+
+  ModuleResult result = SyncDecodeWasmModule(
+      isolate, bytes_copy.start(), bytes_copy.end(), false, kWasmOrigin);
   if (result.failed()) {
     thrower->CompileFailed("Wasm decoding failed", result);
     return {};
@@ -823,7 +828,7 @@ MaybeHandle<WasmModuleObject> wasm::SyncCompile(Isolate* isolate,
   // {CompileToModuleObject}.
   Handle<Code> centry_stub = CEntryStub(isolate, 1).GetCode();
   ModuleCompiler compiler(isolate, std::move(result.val), centry_stub);
-  return compiler.CompileToModuleObject(thrower, bytes, Handle<Script>(),
+  return compiler.CompileToModuleObject(thrower, bytes_copy, Handle<Script>(),
                                         Vector<const byte>());
 }