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

test/unittests/wasm/encoder-unittest.cc

Index: test/unittests/wasm/encoder-unittest.cc
diff --git a/test/unittests/wasm/encoder-unittest.cc b/test/unittests/wasm/encoder-unittest.cc
index 47885e697d243c3e15772c12cbaf9df979214cfe..4e51aa65f13080eac3287a397f878d13811854cd 100644
--- a/test/unittests/wasm/encoder-unittest.cc
+++ b/test/unittests/wasm/encoder-unittest.cc
@@ -23,6 +23,14 @@ class EncoderTest : public TestWithZone {
   }
 };
 
+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