[Smart Lock] Add a setting to require close proximity in order for unlocking to work.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 2be1cb77c460f9bcf289d7f62dde633fb848c8d6..35164f74857ef4e0593be60d8d809bad9276adff 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -10093,9 +10093,12 @@ Chrome ran out of memory.
         <message name="IDS_OPTIONS_EASY_UNLOCK_SETUP_BUTTON" desc="The label of the button to set up Easy Unlock section on the settings page.">
           Set up Smart Lock
         </message>
-        <message name="IDS_OPTIONS_EASY_UNLOCK_DESCRIPTION" desc="The text that describs what Easy Unlock does.">
+        <message name="IDS_OPTIONS_EASY_UNLOCK_DESCRIPTION" desc="The text that describes what Easy Unlock does.">
           Your <ph name="DEVICE_TYPE">$1<ex>Chromebook</ex></ph> will be unlocked when your Android phone is unlocked and nearby.
         </message>
+        <message name="IDS_OPTIONS_EASY_UNLOCK_REQUIRE_PROXIMITY_LABEL" desc="The text label that describes the checkbox that controls whether the user's Android phone must be in close proximity to the Chromebook in order to unlock it..">
+          Allow unlocking this <ph name="DEVICE_TYPE">$1<ex>Chromebook</ex></ph> only when the phone is ZERO feet away.

[Tim Song, 2014/11/03 19:16:13]

Since this string is not finalized, let's remove the number, and just say
something like "when the phone is very close." in case we can't merge strings
back.

[Ilya Sherman, 2014/11/04 03:03:43]

I went with "only when the phone is within an arm's length away", which is
roughly the wording that Xiaowen suggested in person (specifically, she
recommended using the phrase "arm's length").  Not sure about using both
"within" and "away", though -- that feels a bit clunky.  Do you have any
suggestions on how to refine?

[Tim Song, 2014/11/04 20:40:23]

Given the lack of testing with various combinations of Chromebooks and phones, I
feel hesitant about quantifying this distance even by analogy. However, as long
as this is behind a flag, I think the wording is fine.

+        </message>
         <message name="IDS_OPTIONS_EASY_UNLOCK_TURN_OFF_BUTTON" desc="The label of the button to disable Easy unlock on the settings page and the turn off Easy unlock dialog.">
           Turn off
         </message>