Add CombinedDesktopMediaList class

chrome/browser/media/desktop_media_list_base.h

Index: chrome/browser/media/desktop_media_list_base.h
diff --git a/chrome/browser/media/desktop_media_list_base.h b/chrome/browser/media/desktop_media_list_base.h
index 499571bf952be6fa405a9cdb11833c55fa313242..36a05b09b155a7beeef3201702a091410a802310 100644
--- a/chrome/browser/media/desktop_media_list_base.h
+++ b/chrome/browser/media/desktop_media_list_base.h
@@ -11,11 +11,18 @@
 // Thumbnail size is 100*100 pixels
 static const int kDefaultThumbnailSize = 100;
 
-// Base class for DesktopMedaiList implementations. Implements logic shared
+// Base class for DesktopMediaList implementations. Implements logic shared
 // between implementations. Specifically it's responsible for keeping current
 // list of sources and calling the observer when the list changes.
 class DesktopMediaListBase : public DesktopMediaList {
  public:
+  struct SourceDescription {
+    SourceDescription(content::DesktopMediaID id, const base::string16& name);
+
+    content::DesktopMediaID id;
+    base::string16 name;
+  };
+
   explicit DesktopMediaListBase(base::TimeDelta update_period);
   ~DesktopMediaListBase() override;
 
@@ -28,13 +35,6 @@ class DesktopMediaListBase : public DesktopMediaList {
   const Source& GetSource(int index) const override;
 
  protected:
-  struct SourceDescription {
-    SourceDescription(content::DesktopMediaID id, const base::string16& name);
-
-    content::DesktopMediaID id;
-    base::string16 name;
-  };
-
   virtual void Refresh() = 0;
 
   // Update source media list to observer.