ValueSerializer: Take advantage of fast elements in dense array serialization.

test/unittests/value-serializer-unittest.cc

 // Copyright 2016 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 "src/value-serializer.h"
 
 #include <algorithm>
 #include <string>
 
 #include "include/v8.h"
@@ skipping 929 matching lines @@
       "(() => {"
       "  var x = [1, { get a() { x.length = 0; }}, 3, 4];"
       "  return x;"
       "})()",
       [this](Local<Value> value) {
         ASSERT_TRUE(value->IsArray());
         ASSERT_EQ(4, Array::Cast(*value)->Length());
         EXPECT_TRUE(EvaluateScriptForResultBool("result[0] === 1"));
         EXPECT_TRUE(EvaluateScriptForResultBool("!result.hasOwnProperty(2)"));
       });
+  // The same is true if the length is shortened, but there are still items
+  // remaining.
+  RoundTripTest(
+      "(() => {"
+      "  var x = [1, { get a() { x.length = 3; }}, 3, 4];"
+      "  return x;"
+      "})()",
+      [this](Local<Value> value) {
+        ASSERT_TRUE(value->IsArray());
+        ASSERT_EQ(4, Array::Cast(*value)->Length());
+        EXPECT_TRUE(EvaluateScriptForResultBool("result[2] === 3"));
+        EXPECT_TRUE(EvaluateScriptForResultBool("!result.hasOwnProperty(3)"));
+      });
   // Same for sparse arrays.
   RoundTripTest(
       "(() => {"
       "  var x = [1, { get a() { x.length = 0; }}, 3, 4];"
       "  x.length = 1000;"
       "  return x;"
       "})()",
       [this](Local<Value> value) {
         ASSERT_TRUE(value->IsArray());
         ASSERT_EQ(1000, Array::Cast(*value)->Length());
         EXPECT_TRUE(EvaluateScriptForResultBool("result[0] === 1"));
         EXPECT_TRUE(EvaluateScriptForResultBool("!result.hasOwnProperty(2)"));
       });
+  RoundTripTest(
+      "(() => {"
+      "  var x = [1, { get a() { x.length = 3; }}, 3, 4];"
+      "  x.length = 1000;"
+      "  return x;"
+      "})()",
+      [this](Local<Value> value) {
+        ASSERT_TRUE(value->IsArray());
+        ASSERT_EQ(1000, Array::Cast(*value)->Length());
+        EXPECT_TRUE(EvaluateScriptForResultBool("result[2] === 3"));
+        EXPECT_TRUE(EvaluateScriptForResultBool("!result.hasOwnProperty(3)"));
+      });
   // If a getter makes a property non-enumerable, it should still be enumerated
   // as enumeration happens once before getters are invoked.
   RoundTripTest(
       "(() => {"
       "  var x = [{ get a() {"
       "    Object.defineProperty(x, '1', { value: 3, enumerable: false });"
       "  }}, 2];"
       "  return x;"
       "})()",
       [this](Local<Value> value) {
@@ skipping 1021 matching lines @@
 }
 
 TEST_F(ValueSerializerTestWithSharedArrayBufferTransfer,
        SharedArrayBufferMustBeTransferred) {
   // A SharedArrayBuffer which was not marked for transfer should fail encoding.
   InvalidEncodeTest("new SharedArrayBuffer(32)");
 }
 
 }  // namespace
 }  // namespace v8