Add login screen locale and input method device policies

ui/base/ime/chromeos/input_method_manager.h

Index: ui/base/ime/chromeos/input_method_manager.h
diff --git a/ui/base/ime/chromeos/input_method_manager.h b/ui/base/ime/chromeos/input_method_manager.h
index 69531425da3f47b1443a1431e8544a02ada22f47..775d8fa65dceee73ae7115e83ca4420ddab2e6d9 100644
--- a/ui/base/ime/chromeos/input_method_manager.h
+++ b/ui/base/ime/chromeos/input_method_manager.h
@@ -213,6 +213,19 @@ class UI_BASE_IME_EXPORT InputMethodManager {
     virtual bool ReplaceEnabledInputMethods(
         const std::vector<std::string>& new_active_input_method_ids) = 0;
 
+    // Sets the currently allowed keyboard layout input methods (e.g. due to
+    // policy). Invalid input method ids are ignored. Passing an empty vector
+    // means that all keyboard layout input methods are allowed, which is the
+    // default.
+    // When allowed input methods are set, these are also automatically enabled.
+    virtual bool SetAllowedKeyboardLayoutInputMethods(

[Yuki, 2017/01/31 15:18:29]

nit: "keyboard layout input method" sounds a bit weird to me because "input
method" in a concept containing direct input (with a variety of keyboard
layouts) and non-direct input (such as Chinese/Japanese/Korean).

I'd recommend to rename this to SetAllowedInputMethods, which I think is more
consistent with other parts.  (Please update the comment, too, if you're going
to rename this.)

[pmarko, 2017/02/01 10:04:12]

Good point, the naming indeed is a little weird.

My idea was to actually only restrict physical keyboard layouts (i.e. don't stop
people from using some IME extension they might want), that's why I included
"KeyboardLayout" in there.
That's also why InputMethodManagerImpl::IsInputMethodAllowed checks for
IsKeyboardLayout.

Currently, this should be irrelevant, as it's only used on the login screen, but
if we ever extend the policy to user sessions, I didn't want to restrict
extensions which the user might need e.g. for accessibility.

Would you be fine with SetAllowedKeyboardLayouts, i.e. strip the InputMethod
part as it is redundant?
Or do you feel that restricting xkb keyboard layouts only is a dubious goal and
we should just treat all input methods the same way?

[Yuki, 2017/02/01 12:12:19]

My personal preference is to use a general tool with a specific policy. 
Ideally, "policy" should be injected as config data, etc., and better to avoid
hard-coding the policy.  Otherwise, if the policy changed, we would need to
change the design drastically.  I'd recommend to make this interface not depend
on a specific policy, and to implement a specific implementation class (i.e.
InputMethodManagerImpl::StateImpl) with a specific policy.

[pmarko, 2017/02/01 14:07:57]

Done.

+        const std::vector<std::string>& allowed_input_method_ids) = 0;
+
+    // Returns the currently allowed keyboard layout input methods, as set by
+    // SetAllowedKeyboardLayoutInputMethodIds.
+    virtual const std::vector<std::string>&
+    GetAllowedKeyboardLayoutInputMethods() = 0;

[Yuki, 2017/01/31 15:18:29]

nit: Ditto.

[pmarko, 2017/02/01 14:07:57]

Done.

+
    protected:
     friend base::RefCounted<InputMethodManager::State>;