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

test/mjsunit/wasm/wasm-constants.js

 // 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.
 
 // Flags: --expose-wasm
 
 function bytes() {
   var buffer = new ArrayBuffer(arguments.length);
   var view = new Uint8Array(buffer);
   for (var i = 0; i < arguments.length; i++) {
     var val = arguments[i];
     if ((typeof val) == "string") val = val.charCodeAt(0);
     view[i] = val | 0;
   }
   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;
 var kDeclFunctions = 0x02;
 var kDeclGlobals = 0x03;
 var kDeclDataSegments = 0x04;
 var kDeclFunctionTable = 0x05;
 var kDeclStartFunction = 0x07;
 var kDeclImportTable = 0x08;
 var kDeclExportTable = 0x09;
@@ skipping 215 matching lines @@
       }
       threwException = false;
     } catch (e) {
       assertEquals("string", typeof e);
       assertEquals(kTrapMsgs[trap], e);
       // Success.
       return;
     }
     throw new MjsUnitAssertionError("Did not trap, expected: " + kTrapMsgs[trap]);
 }