chromeos: move --mus and --mash to features

This is mildly tricky as --mash implies the window service too. So,
there is now a function test if mus (meaning either Mus or Mash is
enabled). This nukes IsMusHostingViz() and instead queries the
feature directly. Additionally I've nuked supplying how to configure
aura in init params (as it can be determined from features directly).

BUG=800357
TEST=covered by tests

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Ib51c5135caf9df4b4e430ccd20b63a4bea6dae93
Reviewed-on: https://chromium-review.googlesource.com/927360
Reviewed-by: Mark Pearson <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Sadrul Chowdhury <[email protected]>
Commit-Queue: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#538591}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 60c4349..6e6b5ef 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1530,10 +1530,10 @@
      FEATURE_VALUE_TYPE(features::kMultiDeviceApi)},
     {"mus", flag_descriptions::kUseMusName,
      flag_descriptions::kUseMusDescription, kOsCrOS,
-     SINGLE_VALUE_TYPE(switches::kMus)},
+     FEATURE_VALUE_TYPE(features::kMus)},
     {"mash", flag_descriptions::kUseMashName,
      flag_descriptions::kUseMashDescription, kOsCrOS,
-     SINGLE_VALUE_TYPE(switches::kMash)},
+     FEATURE_VALUE_TYPE(features::kMash)},
     {"show-taps", flag_descriptions::kShowTapsName,
      flag_descriptions::kShowTapsDescription, kOsCrOS,
      SINGLE_VALUE_TYPE(ash::switches::kShowTaps)},
@@ -3792,7 +3792,7 @@
 bool SkipConditionalFeatureEntry(const FeatureEntry& entry) {
   version_info::Channel channel = chrome::GetChannel();
 #if defined(OS_CHROMEOS)
-  // Don't expose --mash on stable channel.
+  // Don't expose mash on stable channel.
   if (!strcmp("mash", entry.internal_name) &&
       channel == version_info::Channel::STABLE) {
     return true;