[wasm] JS API tests for `WebAssembly.validate`

Also ensuring it is validation error to specify more than
one memory import.

BUG=v8:5824

Review-Url: https://codereview.chromium.org/2624853002
Cr-Commit-Position: refs/heads/master@{#42205}

src/wasm/module-decoder.cc

@@ -324,7 +324,11 @@ class ModuleDecoder : public Decoder {
                                      &module->min_mem_pages, &has_max,
                                      kSpecMaxWasmMemoryPages,
                                      &module->max_mem_pages);
+            if (module->has_memory) {
+              error("At most one memory object is supported");
+            } else {
               module->has_memory = true;
+            }
             break;
           }
           case kExternalGlobal: {

src/wasm/wasm-module.cc

@@ -1658,6 +1658,9 @@ class WasmInstanceBuilder {
           break;
         }
         case kExternalMemory: {
+          // Validation should have failed if more than one memory object was
+          // provided.
+          DCHECK(!instance->has_memory_object());
           if (!WasmJs::IsWasmMemoryObject(isolate_, value)) {
             ReportLinkError("memory import must be a WebAssembly.Memory object",
                             index, module_name, import_name);

test/mjsunit/wasm/js-api.js

@@ -41,6 +41,13 @@ let importingModuleBinary = (() => {
   return new Int8Array(builder.toBuffer());
 })();
 
+let moduleBinaryImporting2Memories = (() => {
+  var builder = new WasmModuleBuilder();
+  builder.addImportedMemory("", "memory1");
+  builder.addImportedMemory("", "memory2");
+  return new Int8Array(builder.toBuffer());
+})();
+
 // 'WebAssembly' data property on global object
 let wasmDesc = Object.getOwnPropertyDescriptor(this, 'WebAssembly');
 assertEq(typeof wasmDesc.value, "object");
@@ -478,6 +485,13 @@ assertEq(tbl.length, 2);
 assertErrorMessage(() => tbl.grow(1), Error, /failed to grow table/);
 }
 
+// 'WebAssembly.validate' function
+assertErrorMessage(() => WebAssembly.validate(), TypeError);
+assertErrorMessage(() => WebAssembly.validate("hi"), TypeError);
+assertEq(WebAssembly.validate(emptyModuleBinary), true);
+// TODO: other ways for validate to return false.
+assertEq(WebAssembly.validate(moduleBinaryImporting2Memories), false);
+
 // 'WebAssembly.compile' data property
 let compileDesc = Object.getOwnPropertyDescriptor(WebAssembly, 'compile');
 assertEq(typeof compileDesc.value, "function");