Add PlatformScreenDelegate and start implementation.

services/ui/display/platform_screen.h

Index: services/ui/display/platform_screen.h
diff --git a/services/ui/display/platform_screen.h b/services/ui/display/platform_screen.h
index 4c3aa456b3ea03c789bc09061068134fedf4d037..79c0753a63d4bccbc30a68854758792c69f19369 100644
--- a/services/ui/display/platform_screen.h
+++ b/services/ui/display/platform_screen.h
@@ -9,21 +9,32 @@
 
 #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.
@@ -32,10 +43,12 @@ class PlatformScreen {
   // 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;
 };