Set overflow: auto in StyleResolver::styleForDocument.

third_party/WebKit/Source/web/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 import("//third_party/WebKit/Source/bindings/bindings.gni")
 import("//third_party/WebKit/Source/config.gni")
 import("//third_party/WebKit/Source/core/core.gni")
 import("//third_party/WebKit/Source/modules/modules.gni")
@@ skipping 339 matching lines @@
     "tests/ListenerLeakTest.cpp",
     "tests/MHTMLTest.cpp",
     "tests/MediaElementFillingViewportTest.cpp",
     "tests/NGInlineLayoutTest.cpp",
     "tests/PrerenderingTest.cpp",
     "tests/ProgrammaticScrollTest.cpp",
     "tests/ResizeObserverTest.cpp",
     "tests/RootScrollerTest.cpp",
     "tests/RunAllTests.cpp",
     "tests/ScreenWakeLockTest.cpp",
+    "tests/ScrollbarsTest.cpp",
     "tests/ScrollingCoordinatorTest.cpp",
     "tests/SpinLockTest.cpp",
     "tests/TextFinderTest.cpp",
     "tests/TextSelectionRepaintTest.cpp",
     "tests/TimerPerfTest.cpp",
     "tests/TouchActionTest.cpp",
     "tests/ViewportTest.cpp",
     "tests/VirtualTimeTest.cpp",
     "tests/VisualViewportTest.cpp",
     "tests/WebDocumentSubresourceFilterTest.cpp",
@@ skipping 67 matching lines @@
 
   if (is_android) {
     deps += [
       "//base:base_java",
       "//content/public/android:content_java",
       "//content/shell/android:content_shell_assets",
       "//net/android:net_java",
     ]
   }
 }