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

On Mac, make it a Feature controlled by chrome://flags/#bookmark-apps.
(Currently one needs to "Enable" #disable-new-bookmark-apps which is
confusing). Feature flags have other benefits over command line flags
too (e.g. Finch integration).

On other platforms, it's been on by default for a long time and doesn't
need a disable flag. Hardcoding it to `true` means we have some more
obviously dead code around IDC_CREATE_SHORTCUTS which was never
implemented on Mac, and replaced by bookmark apps elsewhere.

BUG=702551

Review-Url: https://codereview.chromium.org/2765083002
Cr-Commit-Position: refs/heads/master@{#459209}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 272bcd9..79258f9 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1367,12 +1367,10 @@
      IDS_FLAGS_FIRST_RUN_UI_TRANSITIONS_DESCRIPTION, kOsCrOS,
      SINGLE_VALUE_TYPE(chromeos::switches::kEnableFirstRunUITransitions)},
 #endif  // OS_CHROMEOS
-    {"disable-new-bookmark-apps", IDS_FLAGS_NEW_BOOKMARK_APPS_NAME,
-     IDS_FLAGS_NEW_BOOKMARK_APPS_DESCRIPTION,
-     kOsWin | kOsCrOS | kOsLinux | kOsMac,
-     ENABLE_DISABLE_VALUE_TYPE(switches::kEnableNewBookmarkApps,
-                               switches::kDisableNewBookmarkApps)},
 #if defined(OS_MACOSX)
+    {"bookmark-apps", IDS_FLAGS_NEW_BOOKMARK_APPS_NAME,
+     IDS_FLAGS_NEW_BOOKMARK_APPS_DESCRIPTION, kOsMac,
+     FEATURE_VALUE_TYPE(features::kBookmarkApps)},
     {"disable-hosted-apps-in-windows", IDS_FLAGS_HOSTED_APPS_IN_WINDOWS_NAME,
      IDS_FLAGS_HOSTED_APPS_IN_WINDOWS_DESCRIPTION, kOsMac,
      ENABLE_DISABLE_VALUE_TYPE(switches::kEnableHostedAppsInWindows,