[Extensions Toolbar] Cleanup popup logic

Move yet more of the popup logic to be stored in the
platform-abstract ExtensionActionViewController.

BUG=457392

Review URL: https://codereview.chromium.org/911753002

Cr-Commit-Position: refs/heads/master@{#315789}
diff --git a/extensions/browser/extension_host.h b/extensions/browser/extension_host.h
index cd7e6ae78..7ff671c3 100644
--- a/extensions/browser/extension_host.h
+++ b/extensions/browser/extension_host.h
@@ -78,6 +78,9 @@
   // (can be NULL). This happens delayed to avoid locking the UI.
   void CreateRenderViewSoon();
 
+  // Closes this host (results in [possibly asynchronous] deletion).
+  void Close();
+
   // Typical observer interface.
   void AddObserver(ExtensionHostObserver* observer);
   void RemoveObserver(ExtensionHostObserver* observer);
@@ -143,9 +146,6 @@
   // Returns true if we're hosting a background page.
   virtual bool IsBackgroundPage() const;
 
-  // Closes this host (results in deletion).
-  void Close();
-
  private:
   friend class ProcessCreationQueue;