Add flag to hide scrollbars completely.

ui/native_theme/native_theme_switches.cc

Index: ui/native_theme/native_theme_switches.cc
diff --git a/ui/native_theme/native_theme_switches.cc b/ui/native_theme/native_theme_switches.cc
index 873af518985c1dc6226256118424e2a6493dd086..a40821124488e558cc6db910f6d1c31cb6dd62d3 100644
--- a/ui/native_theme/native_theme_switches.cc
+++ b/ui/native_theme/native_theme_switches.cc
@@ -13,6 +13,9 @@ const char kEnableOverlayScrollbar[] = "enable-overlay-scrollbar";
 // Disables overlay scrollbars on Aura or Linux. Does nothing on Mac.
 const char kDisableOverlayScrollbar[] = "disable-overlay-scrollbar";
 
+// Hides scrollbars on Aura, Linux, Android, ChromeOS. Does nothing on Mac.

[skobes, 2016/08/02 17:55:56]

What's the plan for Mac?  Or don't we care?

[Eric Seckler, 2016/08/03 17:34:54]

At the moment, we don't care and will look into this at a later time.

+const char kEnableHiddenScrollbar[] = "enable-hidden-scrollbar";

[skobes, 2016/08/02 17:55:56]

Will there also be a disable flag?  If not, perhaps --hide-scrollbars is
clearer?

[Eric Seckler, 2016/08/03 17:34:54]

Done. I was aiming for consistent naming, but you're right, it was awkward :)

+
 }  // namespace switches
 
 namespace ui {
@@ -21,6 +24,10 @@ bool IsOverlayScrollbarEnabled() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
 
+  // Hidden scrollbars are realized through never-showing overlay scrollbars.
+  if (IsHiddenScrollbarEnabled())
+    return true;
+
   if (command_line.HasSwitch(switches::kDisableOverlayScrollbar))
     return false;
   else if (command_line.HasSwitch(switches::kEnableOverlayScrollbar))
@@ -29,4 +36,14 @@ bool IsOverlayScrollbarEnabled() {
   return false;
 }
 
+bool IsHiddenScrollbarEnabled() {

[skobes, 2016/08/02 17:55:56]

"ShouldHideScrollbars"

[Eric Seckler, 2016/08/03 17:34:54]

Done.

+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+
+  if (command_line.HasSwitch(switches::kEnableHiddenScrollbar))
+    return true;
+
+  return false;
+}
+
 }  // namespace ui