[wasm] Implement correct 2-level namespace for imports.

src/wasm/module-decoder.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 "src/wasm/module-decoder.h"
 
 #include "src/base/functional.h"
 #include "src/base/platform/platform.h"
 #include "src/flags.h"
 #include "src/macro-assembler.h"
@@ skipping 262 matching lines @@
             0,                  // module_name_offset
             0,                  // field_name_offset
             0,                  // field_name_length
             kExternalFunction,  // kind
             0                   // index
         });
         WasmImport* import = &module->import_table.back();
         const byte* pos = pc_;
         import->module_name_offset =
             consume_string(&import->module_name_length, true);
-        if (import->module_name_length == 0) {
-          error(pos, "import module name cannot be NULL");
-        }
         import->field_name_offset =
             consume_string(&import->field_name_length, true);
 
         import->kind = static_cast<WasmExternalKind>(consume_u8("import kind"));
         switch (import->kind) {
           case kExternalFunction: {
             // ===== Imported function =======================================
             import->index = static_cast<uint32_t>(module->functions.size());
             module->num_imported_functions++;
             module->functions.push_back({nullptr,        // sig
@@ skipping 928 matching lines @@
     table.push_back(std::move(func_asm_offsets));
   }
   if (decoder.more()) decoder.error("unexpected additional bytes");
 
   return decoder.toResult(std::move(table));
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8