Move even more from WmShell to Shell

ash/system/chromeos/power/tablet_power_button_controller.cc

Index: ash/system/chromeos/power/tablet_power_button_controller.cc
diff --git a/ash/system/chromeos/power/tablet_power_button_controller.cc b/ash/system/chromeos/power/tablet_power_button_controller.cc
index 56569a52ba4ca438358877f371e0b6d33f359db1..fb8f60ae146dccdd739d91389960918bd9b7a7e9 100644
--- a/ash/system/chromeos/power/tablet_power_button_controller.cc
+++ b/ash/system/chromeos/power/tablet_power_button_controller.cc
@@ -43,7 +43,7 @@ constexpr int kIgnoreRepeatedButtonUpMs = 500;
 // Returns true if device is a convertible/tablet device, otherwise false.
 bool IsTabletModeSupported() {
   MaximizeModeController* maximize_mode_controller =
-      WmShell::Get()->maximize_mode_controller();
+      Shell::Get()->maximize_mode_controller();
   return maximize_mode_controller &&
          maximize_mode_controller->CanEnterMaximizeMode();
 }
@@ -51,7 +51,7 @@ bool IsTabletModeSupported() {
 // Returns true if device is currently in tablet/maximize mode, otherwise false.
 bool IsTabletModeActive() {
   MaximizeModeController* maximize_mode_controller =
-      WmShell::Get()->maximize_mode_controller();
+      Shell::Get()->maximize_mode_controller();
   return maximize_mode_controller &&
          maximize_mode_controller->IsMaximizeModeWindowManagerEnabled();
 }