[CrOS MultiDevice] Add string for Back button

Bug: 882647
Change-Id: I358d737e7b2e073d42d1e7da7825a5d0e378a9aa
Reviewed-on: https://chromium-review.googlesource.com/1252841Reviewed-by: Jeremy Klein <jlklein@chromium.org>
Commit-Queue: Josh Nohle <nohle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595282}

chrome/app/chromeos_strings.grdp

@@ -150,6 +150,9 @@
   <message name="IDS_MULTIDEVICE_SETUP_PASSWORD_PAGE_WRONG_PASSWORD_LABEL" desc="Message displayed in the multi-device setup flow when the user has entered an incorrect password.">
     Wrong password
   </message>
+  <message name="IDS_MULTIDEVICE_SETUP_BACK_LABEL" desc="Label for button to navigate back in MultiDevice setup workflow.">
+    Back
+  </message>
   <message name="IDS_MULTIDEVICE_SETUP_SETUP_FAILED_PAGE_HEADER" desc="Header for failed setup page.">
     Better Together setup couldn't complete
   </message>

chrome/browser/ui/webui/chromeos/multidevice_setup/multidevice_setup_localized_strings_provider.cc

@@ -37,6 +37,7 @@ constexpr struct {
   int id;
 } const kLocalizedStringsWithoutPlaceholders[] = {
     {"accept", IDS_MULTIDEVICE_SETUP_ACCEPT_LABEL},
+    {"back", IDS_MULTIDEVICE_SETUP_BACK_LABEL},
     {"cancel", IDS_CANCEL},
     {"done", IDS_DONE},
     {"passwordPageHeader", IDS_MULTIDEVICE_SETUP_PASSWORD_PAGE_HEADER},