[wasm] Provide better stack traces for asm.js code

src/asmjs/asm-wasm-builder.h

Index: src/asmjs/asm-wasm-builder.h
diff --git a/src/asmjs/asm-wasm-builder.h b/src/asmjs/asm-wasm-builder.h
index 9f85dfaf07b97b40436a48c858e525a984a9b3fb..f234abde8ac2e6ab946e0af125fdb3732b0d1265 100644
--- a/src/asmjs/asm-wasm-builder.h
+++ b/src/asmjs/asm-wasm-builder.h
@@ -20,9 +20,14 @@ namespace wasm {
 
 class AsmWasmBuilder {
  public:
+  struct Result {
+    ZoneBuffer* module_bytes;
+    ZoneBuffer* asm_offset_table;
+  };
+
   explicit AsmWasmBuilder(Isolate* isolate, Zone* zone, FunctionLiteral* root,
                           AsmTyper* typer);
-  ZoneBuffer* Run(Handle<FixedArray>* foreign_args);
+  Result Run(Handle<FixedArray>* foreign_args);
 
   static const char* foreign_init_name;
   static const char* single_function_name;