cros: Make both --mus and --mash available in about:flags

* Allow --mus on all channels (canary, dev, beta, stable).
* Allow --mash on everything but stable.
* Ensure only one copy of the --mus flag if the user specifies
  both --mus and --mash. The build will run in --mash mode.

Bug: none
Test: about:flags has both options separately
Change-Id: Ic111189e288a8784718f4df0a99bae865734fe6f
Reviewed-on: https://chromium-review.googlesource.com/891624Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532686}

chrome/app/chrome_main.cc

@@ -49,6 +49,39 @@ int ChromeMain(int argc, const char** argv);
 }
 #endif
 
+namespace {
+
+#if BUILDFLAG(ENABLE_MUS)
+void ConfigureMus(content::ContentMainParams* params) {
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+#if defined(OS_CHROMEOS)
+  // --mash implies --mus, so check it first.
+  if (command_line->HasSwitch(switches::kMash)) {
+    params->create_discardable_memory = false;
+    params->env_mode = aura::Env::Mode::MUS;
+    // Don't add --mus if the user had both --mash and --mus.
+    if (!command_line->HasSwitch(switches::kMus))
+      command_line->AppendSwitch(switches::kMus);
+    command_line->AppendSwitch(switches::kMusHostingViz);
+    return;
+  }
+#endif  // defined(OS_CHROMEOS)
+
+  // In config==mus the ui service runs in process and is shut down well before
+  // the rest of Chrome. Have Chrome create the DiscardableSharedMemoryManager
+  // to ensure the DiscardableSharedMemoryManager is destroyed later on. Doing
+  // this avoids lifetime issues when internal implementation details of
+  // DiscardableSharedMemoryManager assume DiscardableSharedMemoryManager is
+  // long lived.
+  if (command_line->HasSwitch(switches::kMus)) {
+    params->create_discardable_memory = true;
+    params->env_mode = aura::Env::Mode::MUS;
+  }
+}
+#endif  // BUILDFLAG(ENABLE_MUS)
+
+}  // namespace
+
 #if defined(OS_WIN)
 DLLEXPORT int __cdecl ChromeMain(HINSTANCE instance,
                                  sandbox::SandboxInterfaceInfo* sandbox_info,
@@ -105,26 +138,8 @@ int ChromeMain(int argc, const char** argv) {
 #endif  // defined(OS_LINUX) || defined(OS_MACOSX) || defined(OS_WIN)
 
 #if BUILDFLAG(ENABLE_MUS)
-  // In config==mus the ui service runs in process and is shut down well before
-  // the rest of Chrome. Have Chrome create the DiscardableSharedMemoryManager
-  // to ensure the DiscardableSharedMemoryManager is destroyed later on. Doing
-  // this avoids lifetime issues when internal implementation details of
-  // DiscardableSharedMemoryManager assume DiscardableSharedMemoryManager is
-  // long lived.
-  if (command_line->HasSwitch(switches::kMus)) {
-    params.create_discardable_memory = true;
-    params.env_mode = aura::Env::Mode::MUS;
-  }
-#if defined(OS_CHROMEOS)
-  if (command_line->HasSwitch(switches::kMash)) {
-    params.create_discardable_memory = false;
-    params.env_mode = aura::Env::Mode::MUS;
-    base::CommandLine::ForCurrentProcess()->AppendSwitch(switches::kMus);
-    base::CommandLine::ForCurrentProcess()->AppendSwitch(
-        switches::kMusHostingViz);
-  }
-#endif  // defined(OS_CHROMEOS)
-#endif  // BUILDFLAG(ENABLE_MUS)
+  ConfigureMus(&params);
+#endif
 
   int rv = content::ContentMain(params);
 

chrome/browser/about_flags.cc

@@ -512,12 +512,6 @@ const FeatureEntry::Choice kDataSaverPromptChoices[] = {
      chromeos::switches::kDataSaverPromptDemoMode},
 };
 
-const FeatureEntry::Choice kUseMusChoices[] = {
-    {flags_ui::kGenericExperimentChoiceDefault, "", ""},
-    {flag_descriptions::kEnableMusDescription, switches::kMus, ""},
-    {flag_descriptions::kEnableMashDescription, switches::kMash, ""},
-};
-
 const FeatureEntry::Choice kUiShowCompositedLayerBordersChoices[] = {
     {flags_ui::kGenericExperimentChoiceDefault, "", ""},
     {flag_descriptions::kUiShowCompositedLayerBordersRenderPass,
@@ -1523,7 +1517,10 @@ const FeatureEntry kFeatureEntries[] = {
      FEATURE_VALUE_TYPE(features::kMultidevice)},
     {"mus", flag_descriptions::kUseMusName,
      flag_descriptions::kUseMusDescription, kOsCrOS,
-     MULTI_VALUE_TYPE(kUseMusChoices)},
+     SINGLE_VALUE_TYPE(switches::kMus)},
+    {"mash", flag_descriptions::kUseMashName,
+     flag_descriptions::kUseMashDescription, kOsCrOS,
+     SINGLE_VALUE_TYPE(switches::kMash)},
     {"show-taps", flag_descriptions::kShowTapsName,
      flag_descriptions::kShowTapsDescription, kOsCrOS,
      SINGLE_VALUE_TYPE(ash::switches::kShowTaps)},
@@ -3718,11 +3715,9 @@ class FlagsStateSingleton {
 bool SkipConditionalFeatureEntry(const FeatureEntry& entry) {
   version_info::Channel channel = chrome::GetChannel();
 #if defined(OS_CHROMEOS)
-  // Only expose --mash/--mus on unstable channels and developer builds.
-  if (!strcmp("mus", entry.internal_name) &&
-      channel != version_info::Channel::DEV &&
-      channel != version_info::Channel::CANARY &&
-      channel != version_info::Channel::UNKNOWN) {
+  // Don't expose --mash on stable channel.
+  if (!strcmp("mash", entry.internal_name) &&
+      channel == version_info::Channel::STABLE) {
     return true;
   }
 

chrome/browser/flag_descriptions.cc

@@ -2748,12 +2748,15 @@ const char kUiDevToolsDescription[] =
     "Enables inspection of native UI elements. For local inspection use "
     "chrome://inspect#other";
 
-const char kUseMusName[] = "Mus";
-const char kUseMusDescription[] = "Enable the Mojo UI service.";
-const char kEnableMashDescription[] =
-    "Mash (UI, Chrome and ash in separate services)";
-const char kEnableMusDescription[] =
-    "Mus (UI in separate service, Chrome and ash in same service)";
+const char kUseMusName[] = "Mojo UI service (mus)";
+const char kUseMusDescription[] =
+    "Handles input events, display configuration, and windowing in a mojo "
+    "service on a thread in the browser process.";
+
+const char kUseMashName[] = "Out-of-process system UI (mash)";
+const char kUseMashDescription[] =
+    "Runs the mojo UI service (mus) and the ash window manager and system UI "
+    "in a separate process.";
 
 // TODO(mcasas): remove after https://crbug.com/771345.
 const char kUseMonitorColorSpaceName[] = "Use monitor color space";

chrome/browser/flag_descriptions.h

@@ -1684,8 +1684,9 @@ extern const char kUiDevToolsDescription[];
 
 extern const char kUseMusName[];
 extern const char kUseMusDescription[];
-extern const char kEnableMashDescription[];
-extern const char kEnableMusDescription[];
+
+extern const char kUseMashName[];
+extern const char kUseMashDescription[];
 
 extern const char kUseMonitorColorSpaceName[];
 extern const char kUseMonitorColorSpaceDescription[];