[wasm] Refactor encoder.h to use a proper buffer and remove OldFunctions section.

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 1151 matching lines @@
     mod.globals.push_back({0, 0, mem_type, 0, false});
     CHECK(mod.globals.size() <= 127);
     return static_cast<byte>(mod.globals.size() - 1);
   }
   byte AddSignature(FunctionSig* sig) {
     mod.signatures.push_back(sig);
     CHECK(mod.signatures.size() <= 127);
     return static_cast<byte>(mod.signatures.size() - 1);
   }
   byte AddFunction(FunctionSig* sig) {
-    mod.functions.push_back({sig,      // sig
-                             0,        // func_index
-                             0,        // sig_index
-                             0,        // name_offset
-                             0,        // name_length
-                             0,        // code_start_offset
-                             0,        // code_end_offset
-                             false});  // exported
+    mod.functions.push_back({sig,  // sig
+                             0,    // func_index
+                             0,    // sig_index
+                             0,    // name_offset
+                             0,    // name_length
+                             0,    // code_start_offset
+                             0});  // code_end_offset
     CHECK(mod.functions.size() <= 127);
     return static_cast<byte>(mod.functions.size() - 1);
   }
   byte AddImport(FunctionSig* sig) {
     mod.import_table.push_back({sig,  // sig
                                 0,    // sig_index
                                 0,    // module_name_offset
                                 0,    // module_name_length
                                 0,    // function_name_offset
                                 0});  // function_name_length
@@ skipping 1245 matching lines @@
   LocalTypeMap map = Expand(decls);
   size_t pos = 0;
   pos = ExpectRun(map, pos, kAstF32, 5);
   pos = ExpectRun(map, pos, kAstI32, 1337);
   pos = ExpectRun(map, pos, kAstI64, 212);
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8