Add ManagePasswordItemViewController and unit tests.

components/password_manager/core/common/password_manager_ui.h

Index: components/password_manager/core/common/password_manager_ui.h
diff --git a/components/password_manager/core/common/password_manager_ui.h b/components/password_manager/core/common/password_manager_ui.h
index 2728c61dd9816851e8b829d8478dee2a94da3847..f09ccf7d2c50a53a467724562790795ab5664544 100644
--- a/components/password_manager/core/common/password_manager_ui.h
+++ b/components/password_manager/core/common/password_manager_ui.h
@@ -37,6 +37,15 @@ enum State {
   BLACKLIST_STATE,
 };
 
+// The position of a password item in a list of credentials.
+enum PasswordItemPosition {
+  // The password item is the first in the list.
+  FIRST_ITEM,
+
+  // The password item is not the first item in the list.
+  SUBSEQUENT_ITEM,
+};
+
 // Returns true if |state| represents a pending password.
 bool IsPendingState(State state);