[wasm] Fix confusingly named variables

... and fix comments which I accidentally changed back to an old version
in https://crrev.com/c/2011086/.

R=jkummerow@chromium.org

Bug: chromium:667678
Change-Id: I2a801d9775bd2362290c5d1caaf5b9e24a9bd54d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2015241
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65968}

src/asmjs/asm-js.cc

@@ -410,9 +410,9 @@ MaybeHandle<Object> AsmJs::InstantiateAsmWasm(Isolate* isolate,
   }
 
   wasm::ErrorThrower thrower(isolate, "AsmJs::Instantiate");
-  MaybeHandle<Object> maybe_module_object =
+  MaybeHandle<WasmInstanceObject> maybe_instance =
       wasm_engine->SyncInstantiate(isolate, &thrower, module, foreign, memory);
-  if (maybe_module_object.is_null()) {
+  if (maybe_instance.is_null()) {
     // An exception caused by the module start function will be set as pending
     // and bypass the {ErrorThrower}, this happens in case of a stack overflow.
     if (isolate->has_pending_exception()) isolate->clear_pending_exception();
@@ -427,7 +427,7 @@ MaybeHandle<Object> AsmJs::InstantiateAsmWasm(Isolate* isolate,
     return MaybeHandle<Object>();
   }
   DCHECK(!thrower.error());
-  Handle<Object> module_object = maybe_module_object.ToHandleChecked();
+  Handle<WasmInstanceObject> instance = maybe_instance.ToHandleChecked();
 
   ReportInstantiationSuccess(script, position,
                              instantiate_timer.Elapsed().InMillisecondsF());
@@ -435,7 +435,7 @@ MaybeHandle<Object> AsmJs::InstantiateAsmWasm(Isolate* isolate,
   Handle<Name> single_function_name(
       isolate->factory()->InternalizeUtf8String(AsmJs::kSingleFunctionName));
   MaybeHandle<Object> single_function =
-      Object::GetProperty(isolate, module_object, single_function_name);
+      Object::GetProperty(isolate, instance, single_function_name);
   if (!single_function.is_null() &&
       !single_function.ToHandleChecked()->IsUndefined(isolate)) {
     return single_function;
@@ -443,7 +443,7 @@ MaybeHandle<Object> AsmJs::InstantiateAsmWasm(Isolate* isolate,
 
   Handle<String> exports_name =
       isolate->factory()->InternalizeUtf8String("exports");
-  return Object::GetProperty(isolate, module_object, exports_name);
+  return Object::GetProperty(isolate, instance, exports_name);
 }
 
 }  // namespace internal

src/wasm/wasm-module.cc

@@ -597,13 +597,14 @@ int GetSourcePosition(const WasmModule* module, uint32_t func_index,
   DCHECK_EQ(is_asmjs_module(module),
             module->asm_js_offset_information != nullptr);
   if (!is_asmjs_module(module)) {
-    // for non-asm.js modules, we just add the function's start offset
+    // For non-asm.js modules, we just add the function's start offset
     // to make a module-relative position.
     return byte_offset + GetWasmFunctionOffset(module, func_index);
   }
 
   // asm.js modules have an additional offset table that must be searched.
-  // The passed func_index excludes imported functions.
+  // Note: {AsmJsOffsetInformation::GetSourcePosition} expects the function
+  // index relative to the first non-imported function.
   DCHECK_LE(module->num_imported_functions, func_index);
   return module->asm_js_offset_information->GetSourcePosition(
       func_index - module->num_imported_functions, byte_offset,