[wasm] Support a two-level namespace for imports.

src/wasm/wasm-module.h

 // 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.
 
 #ifndef V8_WASM_MODULE_H_
 #define V8_WASM_MODULE_H_
 
 #include "src/wasm/wasm-opcodes.h"
 #include "src/wasm/wasm-result.h"
 
@@ skipping 123 matching lines @@
 
   WasmModule();
 
   // Get a pointer to a string stored in the module bytes representing a name.
   const char* GetName(uint32_t offset) const {
     if (offset == 0) return "<?>";  // no name.
     CHECK(BoundsCheck(offset, offset + 1));
     return reinterpret_cast<const char*>(module_start + offset);
   }
 
+  // Get a pointer to a string stored in the module bytes representing a name.
+  const char* GetNameOrNull(uint32_t offset) const {
+    if (offset == 0) return nullptr;  // no name.
+    CHECK(BoundsCheck(offset, offset + 1));
+    return reinterpret_cast<const char*>(module_start + offset);
+  }
+
   // Checks the given offset range is contained within the module bytes.
   bool BoundsCheck(uint32_t start, uint32_t end) const {
     size_t size = module_end - module_start;
     return start < size && end < size;
   }
 
   // Creates a new instantiation of the module in the given isolate.
   MaybeHandle<JSObject> Instantiate(Isolate* isolate, Handle<JSObject> ffi,
                                     Handle<JSArrayBuffer> memory);
 };
@@ skipping 102 matching lines @@
 
 // For testing. Decode, verify, and run the last exported function in the
 // given decoded module.
 int32_t CompileAndRunWasmModule(Isolate* isolate, WasmModule* module);
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_MODULE_H_