Hardcode extensions::util::IsNewBookmarkAppsEnabled() to true, except on Mac.

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index aa0fee8c2f08847b4a5645c8e42ef9096e57355b..2d1424910b97f6ba8fe0c56efa2213193f35cb8f 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -1862,7 +1862,6 @@ void ChromeContentBrowserClient::AppendExtraCommandLineSwitches(
       switches::kDisableBundledPpapiFlash,
       switches::kDisableCastStreamingHWEncoding,
       switches::kDisableJavaScriptHarmonyShipping,
-      switches::kDisableNewBookmarkApps,

[tapted, 2017/03/22 02:34:02]

Using base::Feature allows this stuff to happen automatically when
RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(..) does
BrowserChildProcessHostImpl::CopyFeatureAndFieldTrialFlags(..)

       switches::kEnableBenchmarking,
       switches::kEnableDistillabilityService,
       switches::kEnableNaCl,
@@ -1871,7 +1870,6 @@ void ChromeContentBrowserClient::AppendExtraCommandLineSwitches(
       switches::kEnableNaClNonSfiMode,
 #endif
       switches::kEnableNetBenchmarking,
-      switches::kEnableNewBookmarkApps,
 #if !defined(DISABLE_NACL)
       switches::kForcePNaClSubzero,
 #endif