[wasm] Fix EnsureSpace in the ZoneBuffer of the wasm encoder.

test/unittests/wasm/encoder-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 "src/wasm/ast-decoder.h"
 #include "src/wasm/encoder.h"
 
 #include "test/cctest/wasm/test-signatures.h"
 
 namespace v8 {
 namespace internal {
 namespace wasm {
 
 class EncoderTest : public TestWithZone {
  protected:
   void AddLocal(WasmFunctionBuilder* f, LocalType type) {
     uint16_t index = f->AddLocal(type);
     f->EmitGetLocal(index);
   }
 };
 
+TEST_F(EncoderTest, Regression_647329) {
+  // Test crashed with asan.
+  ZoneBuffer buffer(zone());
+  const size_t kSize = ZoneBuffer::kInitialSize * 3 + 4096 + 100;
+  byte data[kSize];
+  buffer.write(data, kSize);
+}
+
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8