Add a basic functionality to the force-saving menu item.

components/autofill/content/common/autofill_messages.h

Index: components/autofill/content/common/autofill_messages.h
diff --git a/components/autofill/content/common/autofill_messages.h b/components/autofill/content/common/autofill_messages.h
index 4c3ec108c7c26621c2dbda6e0362080c3a723184..b4d3351101e81894bee70be861f41750e229484e 100644
--- a/components/autofill/content/common/autofill_messages.h
+++ b/components/autofill/content/common/autofill_messages.h
@@ -187,6 +187,11 @@ IPC_MESSAGE_ROUTED2(AutofillMsg_PreviewPasswordSuggestion,
                     base::string16 /* username */,
                     base::string16 /* password */)
 
+// Tells the renderer to find the focused password form (assuming it exists).
+// Renderer is expected to respond with the message
+// |AutofillHostMsg_FocusedPasswordFormFound|.
+IPC_MESSAGE_ROUTED0(AutofillMsg_FindFocusedPasswordForm)
+
 // Tells the renderer that this password form is not blacklisted.  A form can
 // be blacklisted if a user chooses "never save passwords for this site".
 IPC_MESSAGE_ROUTED1(AutofillMsg_FormNotBlacklisted,
@@ -338,3 +343,7 @@ IPC_MESSAGE_ROUTED5(
 IPC_MESSAGE_ROUTED2(AutofillHostMsg_SetDataList,
                     std::vector<base::string16> /* values */,
                     std::vector<base::string16> /* labels */)
+
+// Inform the browser which password form is currently focused.

[Mike West, 2015/05/29 07:24:49]

What does it return if there is not a password form currently focused?

[msramek, 2015/05/29 11:57:21]

My original intention was that if there is no form, this message would never be
sent (thus, ContentPasswordManagerDriver would never get the response, and so
nothing would happen).

However, it might be helpful to return an empty |autofill::PasswordForm|. The
password manager will be able to handle this as an error and show an error
message in the bubble. How exactly this would work is still up to discussion
with UI, but since the user made an explicit action, we shouldn't just fail
silently.

+IPC_MESSAGE_ROUTED1(AutofillHostMsg_FocusedPasswordFormFound,
+                    autofill::PasswordForm)