Remove unused Extension::InstallType

extensions/common/extension.h

Index: extensions/common/extension.h
diff --git a/extensions/common/extension.h b/extensions/common/extension.h
index 9bc9c632cd9b981be7fef0523a39885231fd8600..554ec29743c112b9be7d2fdd82837a6a4739ef2e 100644
--- a/extensions/common/extension.h
+++ b/extensions/common/extension.h
@@ -101,14 +101,6 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
     DISABLE_REMOTE_INSTALL = 1 << 11
   };
 
-  enum InstallType {
-    INSTALL_ERROR,
-    DOWNGRADE,
-    REINSTALL,
-    UPGRADE,
-    NEW_INSTALL
-  };
-
   // A base class for parsed manifest data that APIs want to store on
   // the extension. Related to base::SupportsUserData, but with an immutable
   // thread-safe interface to match Extension.