[wasm] Implement official wasm text format

src/wasm/wasm-module.h

Index: src/wasm/wasm-module.h
diff --git a/src/wasm/wasm-module.h b/src/wasm/wasm-module.h
index 2dded1e1c411bd05d0d6a4a37d4341cb2f0ced5f..8074d34539c6d0ab97eea3b38823691d7878b028 100644
--- a/src/wasm/wasm-module.h
+++ b/src/wasm/wasm-module.h
@@ -390,6 +390,7 @@ Handle<Script> GetScript(Handle<JSObject> instance);
 // Returns the disassembly string and a list of <byte_offset, line, column>
 // entries, mapping wasm byte offsets to line and column in the disassembly.
 // The list is guaranteed to be ordered by the byte_offset.
+// Returns an empty string and empty vector if the function index is invalid.
 std::pair<std::string, std::vector<std::tuple<uint32_t, int, int>>>
 DisassembleFunction(Handle<WasmCompiledModule> compiled_module, int func_index);