Enable TouchpadOverscrollHistoryNavigation on CrOS

In crrev.com/c/1013221, we want to disable TouchpadOverscrollHistoryNavigation
on Windows and Linux. But we also disable it on CrOS because I forgot checking
OS_CHROMEOS. In this patch, we enable TouchpadOverscrollHistoryNavigation on
OS_CHROMEOS which is same as today stable.

TouchpadOverscrollHistoryNavigation is Aura only, OS_MACOSX does not check
this flag.

Bug: 838741
Change-Id: Ib9362bc74af1cb800fab665079017fbcb7880402
Reviewed-on: https://chromium-review.googlesource.com/1039867Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555799}

content/public/common/content_features.cc

@@ -40,13 +40,14 @@ const base::Feature kAsyncWheelEvents{"AsyncWheelEvents",
 const base::Feature kAudioServiceOutOfProcess{
     "AudioServiceOutOfProcess", base::FEATURE_DISABLED_BY_DEFAULT};
 
-// Allows swipe left/right from touchpad change browser navigation.
+// Allows swipe left/right from touchpad change browser navigation. Currently
+// only enabled by default on CrOS.
 const base::Feature kTouchpadOverscrollHistoryNavigation {
   "TouchpadOverscrollHistoryNavigation",
-#if defined(OS_WIN) || defined(OS_LINUX)
-      base::FEATURE_DISABLED_BY_DEFAULT
-#else
+#if defined(OS_CHROMEOS)
       base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
 #endif
 };