[wasm] Fix race when assigning {NativeModule} ids.

R=clemensh@chromium.org
BUG=chromium:801878

Change-Id: I32a3cf3a63dfe073a06066f1db2fb32eb739f153
Reviewed-on: https://chromium-review.googlesource.com/883367Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50836}

src/wasm/wasm-code-manager.cc

@@ -30,7 +30,6 @@ namespace internal {
 namespace wasm {
 
 namespace {
-size_t native_module_ids = 0;
 
 #if V8_TARGET_ARCH_X64
 #define __ masm->
@@ -75,6 +74,7 @@ void PatchTrampolineAndStubCalls(
                                    SKIP_ICACHE_FLUSH);
   }
 }
+
 }  // namespace
 
 DisjointAllocationPool::DisjointAllocationPool(Address start, Address end) {
@@ -271,10 +271,12 @@ WasmCode::~WasmCode() {
   }
 }
 
+base::AtomicNumber<size_t> NativeModule::next_id_;
+
 NativeModule::NativeModule(uint32_t num_functions, uint32_t num_imports,
                            bool can_request_more, VirtualMemory* mem,
                            WasmCodeManager* code_manager)
-    : instance_id(native_module_ids++),
+    : instance_id(next_id_.Increment(1)),
       code_table_(num_functions),
       num_imported_functions_(num_imports),
       free_memory_(reinterpret_cast<Address>(mem->address()),

src/wasm/wasm-code-manager.h

@@ -274,7 +274,7 @@ class V8_EXPORT_PRIVATE NativeModule final {
     }
   };
 
-  static base::AtomicNumber<uint32_t> next_id_;
+  static base::AtomicNumber<size_t> next_id_;
   NativeModule(const NativeModule&) = delete;
   NativeModule& operator=(const NativeModule&) = delete;
   NativeModule(uint32_t num_functions, uint32_t num_imports,