[wasm] Add a magic word and a version number to the binary.

test/mjsunit/wasm/wasm-constants.js

Index: test/mjsunit/wasm/wasm-constants.js
diff --git a/test/mjsunit/wasm/wasm-constants.js b/test/mjsunit/wasm/wasm-constants.js
index 861ffa562c030db9ec4bd78b57d51d5c7b748745..f8558fced8ea9bedfb607fb44202ba6917a352cc 100644
--- a/test/mjsunit/wasm/wasm-constants.js
+++ b/test/mjsunit/wasm/wasm-constants.js
@@ -15,6 +15,38 @@ function bytes() {
   return buffer;
 }
 
+// Header declaration constants
+var kWasmH0 = 0;
+var kWasmH1 = 0x61;
+var kWasmH2 = 0x73;
+var kWasmH3 = 0x6d;
+
+var kWasmV0 = 10;
+var kWasmV1 = 0;
+var kWasmV2 = 0;
+var kWasmV3 = 0;
+
+var kHeaderSize = 8;
+
+function bytesWithHeader() {
+  var buffer = new ArrayBuffer(kHeaderSize + arguments.length);
+  var view = new Uint8Array(buffer);
+  view[0] = kWasmH0;
+  view[1] = kWasmH1;
+  view[2] = kWasmH2;
+  view[3] = kWasmH3;
+  view[4] = kWasmV0;
+  view[5] = kWasmV1;
+  view[6] = kWasmV2;
+  view[7] = kWasmV3;
+  for (var i = 0; i < arguments.length; i++) {
+    var val = arguments[i];
+    if ((typeof val) == "string") val = val.charCodeAt(0);
+    view[kHeaderSize + i] = val | 0;
+  }
+  return buffer;
+}
+
 // Section declaration constants
 var kDeclMemory = 0x00;
 var kDeclSignatures = 0x01;