[LayoutNG] Switch NGConstraintSpace to being RefCounted.

third_party/WebKit/Source/core/layout/ng/ng_absolute_utils_test.cc

 // Copyright 2016 The Chromium 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 "core/layout/ng/ng_absolute_utils.h"
 
 #include "core/layout/ng/ng_constraint_space_builder.h"
 #include "core/layout/ng/ng_length_utils.h"
 #include "core/style/ComputedStyle.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 64 matching lines @@
         margin_bottom == NGAuto
             ? Length(LengthType::Auto)
             : Length(margin_bottom.toInt(), LengthType::Fixed));
     style_->setBottom(bottom == NGAuto
                           ? Length(LengthType::Auto)
                           : Length(bottom.toInt(), LengthType::Fixed));
   }
 
   RefPtr<ComputedStyle> style_;
   NGLogicalSize container_size_;
-  Persistent<NGConstraintSpace> ltr_space_;
-  Persistent<NGConstraintSpace> rtl_space_;
-  Persistent<NGConstraintSpace> vertical_lr_space_;
-  Persistent<NGConstraintSpace> vertical_rl_space_;
+  RefPtr<NGConstraintSpace> ltr_space_;
+  RefPtr<NGConstraintSpace> rtl_space_;
+  RefPtr<NGConstraintSpace> vertical_lr_space_;
+  RefPtr<NGConstraintSpace> vertical_rl_space_;
 };
 
 TEST_F(NGAbsoluteUtilsTest, Horizontal) {
   // Test that the equation is computed correctly:
   // left + marginLeft + borderLeft  + paddingLeft +
   // width +
   // right + marginRight + borderRight + paddingRight = container width
 
   // Common setup.
   LayoutUnit left(5);
@@ skipping 373 matching lines @@
   // // Unspecified height becomes estimated, gets clamped to min.
   SetVerticalStyle(NGAuto, NGAuto, NGAuto, NGAuto, NGAuto);
   auto_height = LayoutUnit(20);
   ComputeFullAbsoluteWithChildBlockSize(*ltr_space_, *style_, static_position,
                                         auto_height, &p);
   EXPECT_EQ(min, p.size.width);
 }
 
 }  // namespace
 }  // namespace blink