Device owns the RecoveryUI instance.

Test: mmma -j bootable/recovery
Test: Build and boot into recovery, w/ and w/o enabling quiescent mode
      respectively.
Change-Id: I5d9bb945a6c3c9a3b96199fa0c8071a2f91339a0
diff --git a/device.h b/device.h
index 9510fbe..bf148f5 100644
--- a/device.h
+++ b/device.h
@@ -19,6 +19,7 @@
 
 #include <stddef.h>
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -51,17 +52,15 @@
   explicit Device(RecoveryUI* ui) : ui_(ui) {}
   virtual ~Device() {}
 
-  // Called to obtain the UI object that should be used to display the recovery user interface for
-  // this device. You should not have called Init() on the UI object already, the caller will do
-  // that after this method returns.
+  // Returns a raw pointer to the RecoveryUI object.
   virtual RecoveryUI* GetUI() {
-    return ui_;
+    return ui_.get();
   }
 
-  // Sets the UI object to the given UI. Used to override the default UI in case initialization
-  // failed, or we want a stub for some reason.
-  virtual void SetUI(RecoveryUI* ui) {
-    ui_ = ui;
+  // Resets the UI object to the given UI. Used to override the default UI in case initialization
+  // failed, or we want a different UI for some reason. The device object will take the ownership.
+  virtual void ResetUI(RecoveryUI* ui) {
+    ui_.reset(ui);
   }
 
   // Called when recovery starts up (after the UI has been obtained and initialized and after the
@@ -70,16 +69,15 @@
 
   // Called from the main thread when recovery is at the main menu and waiting for input, and a key
   // is pressed. (Note that "at" the main menu does not necessarily mean the menu is visible;
-  // recovery will be at the main menu with it invisible after an unsuccessful operation [ie OTA
-  // package failure], or if recovery is started with no command.)
+  // recovery will be at the main menu with it invisible after an unsuccessful operation, such as
+  // failed to install an OTA package, or if recovery is started with no command.)
   //
   // 'key' is the code of the key just pressed. (You can call IsKeyPressed() on the RecoveryUI
-  // object you returned from GetUI if you want to find out if other keys are held down.)
+  // object you returned from GetUI() if you want to find out if other keys are held down.)
   //
   // 'visible' is true if the menu is visible.
   //
   // Returns one of the defined constants below in order to:
-  //
   //   - move the menu highlight (kHighlight{Up,Down}: negative value)
   //   - invoke the highlighted item (kInvokeItem: negative value)
   //   - do nothing (kNoAction: negative value)
@@ -87,7 +85,7 @@
   virtual int HandleMenuKey(int key, bool visible);
 
   // Returns the list of menu items (a vector of strings). The menu_position passed to
-  // InvokeMenuItem will correspond to the indexes into this array.
+  // InvokeMenuItem() will correspond to the indexes into this array.
   virtual const std::vector<std::string>& GetMenuItems();
 
   // Performs a recovery action selected from the menu. 'menu_position' will be the index of the
@@ -112,7 +110,8 @@
   }
 
  private:
-  RecoveryUI* ui_;
+  // The RecoveryUI object that should be used to display the user interface for this device.
+  std::unique_ptr<RecoveryUI> ui_;
 };
 
 // The device-specific library must define this function (or the default one will be used, if there