Improve UI for unpacked extensions failing to load

chrome/browser/extensions/unpacked_installer.h

Index: chrome/browser/extensions/unpacked_installer.h
diff --git a/chrome/browser/extensions/unpacked_installer.h b/chrome/browser/extensions/unpacked_installer.h
index 73924a6f6797c27bcef1bb3576d1e4e3f1daf7bc..5d2414987efbdf4d76ae0f56cedccd55d036cad3 100644
--- a/chrome/browser/extensions/unpacked_installer.h
+++ b/chrome/browser/extensions/unpacked_installer.h
@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 
+#include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ -29,6 +30,9 @@ class RequirementsChecker;
 class UnpackedInstaller
     : public base::RefCountedThreadSafe<UnpackedInstaller> {
  public:
+  typedef base::Callback<void(const base::FilePath&, const std::string&)>
+      OnFailureCallback;
+
   static scoped_refptr<UnpackedInstaller> Create(
       ExtensionService* extension_service);
 
@@ -61,6 +65,10 @@ class UnpackedInstaller
     require_modern_manifest_version_ = val;
   }
 
+  void set_on_failure_callback(const OnFailureCallback& callback) {
+    on_failure_callback_ = callback;
+  }
+
  private:
   friend class base::RefCountedThreadSafe<UnpackedInstaller>;
 
@@ -117,6 +125,9 @@ class UnpackedInstaller
   // version.
   bool require_modern_manifest_version_;
 
+  // An optional callback to set in order to be notified of failure.
+  OnFailureCallback on_failure_callback_;
+
   // Gives access to common methods and data of an extension installer.
   ExtensionInstaller installer_;