Add PlatformScreenDelegate and start implementation.

services/ui/display/platform_screen.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_UI_DISPLAY_PLATFORM_SCREEN_H_
 #define SERVICES_UI_DISPLAY_PLATFORM_SCREEN_H_
 
 #include <stdint.h>
 
 #include <memory>
 
-#include "base/callback.h"
-
 namespace gfx {
 class Rect;
 }
 
 namespace display {
 
+class PlatformScreen;
+
+// The PlatformScreen delegate will be informed of changes to the physical
+// and/or virtual displays that are connected.
+class PlatformScreenDelegate {

[sky, 2016/08/25 19:18:43]

It's common chrome practice (and mentioned in style guide) to put interfaces
like this in their own class. Also, make the destructor protected to reinforce
delegate isn't owned by screen.

[kylechar, 2016/08/25 20:26:01]

Done.

+ public:
+  // Called when a display is added.
+  virtual void OnDisplayAdded(PlatformScreen* platform_screen,
+                              int64_t id,
+                              const gfx::Rect& bounds) = 0;
+  // Called when a display is removed.
+  virtual void OnDisplayRemoved(int64_t id) = 0;
+  // Called when a display is modified.
+  virtual void OnDisplayModified(int64_t id, const gfx::Rect& bounds) = 0;
+};
+
 // PlatformScreen provides the necessary functionality to configure all
 // attached physical displays.
 class PlatformScreen {
  public:
-  using ConfiguredDisplayCallback =
-      base::Callback<void(int64_t, const gfx::Rect&)>;
-
   virtual ~PlatformScreen() {}
 
   // Creates a PlatformScreen instance.
   static std::unique_ptr<PlatformScreen> Create();
 
   // Initializes platform specific screen resources.
   virtual void Init() = 0;
 
-  // ConfigurePhysicalDisplay() configures a single physical display and returns
-  // its id and bounds for it via |callback|.
-  virtual void ConfigurePhysicalDisplay(
-      const ConfiguredDisplayCallback& callback) = 0;
+  // Triggers display configuration to start. On device this will trigger the
+  // initial configuration of connected displays. Off device this will create
+  // one or more fake displays and pretend to configure them. A non-null
+  // |delegate| must be provided that will receive notifications when displays
+  // are added, removed or modified.
+  virtual void ConfigureDisplays(PlatformScreenDelegate* delegate) = 0;

[sky, 2016/08/25 19:18:43]

Is there a reason we need both Init and Configure? Can't Init do the config? Or
even have Create() do all this (including taking the delegate).

[kylechar, 2016/08/25 20:26:01]

Yeah, that definitely works. I've merged Init() and ConfigureDisplays() into a
single method. 

We can't have Create perform all of the initialization right now because we wait
for WindowServer to get setup before we start display configuration.

 
   virtual int64_t GetPrimaryDisplayId() const = 0;
 };
 
 }  // namespace display
 
 #endif  // SERVICES_UI_DISPLAY_PLATFORM_SCREEN_H_