Emit 'open-file' event when OS X is trying to open file with the app.

browser/browser_observer.h

@@ -5,6 +5,8 @@
 #ifndef ATOM_BROSER_BROWSER_OBSERVER_H_
 #define ATOM_BROSER_BROWSER_OBSERVER_H_
 
+#include <string>
+
 namespace atom {
 
 class BrowserObserver {
@@ -16,6 +18,11 @@ class BrowserObserver {
   // method will not be called, instead it will call OnWillQuit.
   virtual void OnWindowAllClosed() {}
 
+  // The browser has opened a file by double clicking in Finder or dragging the
+  // file to the Dock icon. (OS X only)
+  virtual void OnOpenFile(bool* prevent_default,
+                          const std::string& file_path) {}
+
  protected:
   virtual ~BrowserObserver() {}
 };