Unify display ids between Display and PlatformDisplay.

services/ui/ws/platform_display.h

Index: services/ui/ws/platform_display.h
diff --git a/services/ui/ws/platform_display.h b/services/ui/ws/platform_display.h
index d7bc2f6033afbc69c355d9835c2638b4eff30fb3..436461d87fed93aa220fbbaa3991b4f6b202830f 100644
--- a/services/ui/ws/platform_display.h
+++ b/services/ui/ws/platform_display.h
@@ -85,7 +85,7 @@ class PlatformDisplay {
   virtual void RequestCopyOfOutput(
       std::unique_ptr<cc::CopyOutputRequest> output_request) = 0;
 
-  virtual int64_t GetDisplayId() const = 0;
+  virtual int64_t GetId() const = 0;
 
   virtual gfx::Rect GetBounds() const = 0;
 
@@ -125,7 +125,7 @@ class DefaultPlatformDisplay : public PlatformDisplay,
   bool IsFramePending() const override;
   void RequestCopyOfOutput(
       std::unique_ptr<cc::CopyOutputRequest> output_request) override;
-  int64_t GetDisplayId() const override;
+  int64_t GetId() const override;
   gfx::Rect GetBounds() const override;
 
  private:
@@ -150,7 +150,7 @@ class DefaultPlatformDisplay : public PlatformDisplay,
   bool IsInHighContrastMode() override;
   const ViewportMetrics& GetViewportMetrics() override;
 
-  int64_t display_id_;
+  int64_t id_;
 
 #if !defined(OS_ANDROID)
   std::unique_ptr<ui::CursorLoader> cursor_loader_;