[wasm] Factor out WasmModuleInstance from ModuleEnv.

test/unittests/wasm/ast-decoder-unittest.cc

 // 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.
 
 #include "test/unittests/test-utils.h"
 
 #include "src/v8.h"
 
 #include "test/cctest/wasm/test-signatures.h"
 
@@ skipping 1186 matching lines @@
   }
 }
 
 
 namespace {
 // A helper for tests that require a module environment for functions and
 // globals.
 class TestModuleEnv : public ModuleEnv {
  public:
   TestModuleEnv() {
-    mem_start = 0;
-    mem_end = 0;
+    instance = nullptr;
     module = &mod;
     linker = nullptr;
-    function_code = nullptr;
     mod.globals = new std::vector<WasmGlobal>;
     mod.signatures = new std::vector<FunctionSig*>;
     mod.functions = new std::vector<WasmFunction>;
   }
   byte AddGlobal(MachineType mem_type) {
     mod.globals->push_back({0, mem_type, 0, false});
     CHECK(mod.globals->size() <= 127);
     return static_cast<byte>(mod.globals->size() - 1);
   }
   byte AddSignature(FunctionSig* sig) {
@@ skipping 1208 matching lines @@
   EXPECT_ARITY(1, kExprF64SConvertI64);
   EXPECT_ARITY(1, kExprF64UConvertI64);
   EXPECT_ARITY(1, kExprF64ConvertF32);
   EXPECT_ARITY(1, kExprF64ReinterpretI64);
   EXPECT_ARITY(1, kExprI32ReinterpretF32);
   EXPECT_ARITY(1, kExprI64ReinterpretF64);
 }
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8