[ios] Add string to material toast

This cl adds strings to the material toast.
Mock: https://screenshot.googleplex.com/Awx9JmcTid6QE3n

A material toast will be shown when Chrome opens in a non-user-expected
mode if incognito mode is disabled/forced by the policy.

Follow up cls are:
- Modify the actions of app long-press menu items when incognito mode is
managed.
- Modify the browser mode when open Chrome from other app when the
incognito mode is managed.

Bug: 1159323
Change-Id: Ic3f17fd9e042e955538d3bc6b4e7f4f6e8a8dd87
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593939
Commit-Queue: Tina Wang <tinazwang@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837801}

ios/chrome/app/strings/ios_strings.grd

@@ -1141,6 +1141,9 @@ Because your account is managed by <ph name="HOSTED_DOMAIN">$1<ex>google.com</ex
       <message name="IDS_IOS_NAVIGATION_BAR_EDIT_BUTTON" desc="Label of the edit button displayed on the navigation bar  [Length: 7em] [iOS only].">
         Edit
       </message>
+      <message name="IDS_IOS_NAVIGATION_BAR_MORE_BUTTON" desc="Label of the more button displayed on the navigation bar  [Length: 7em] [iOS only].">
+        More
+      </message>
       <message name="IDS_IOS_NET_EXPORT_NO_EMAIL_ACCOUNTS_ALERT_MESSAGE" desc="The message of the alert informing a user with no email accounts that they need to configure an email account to send net-export data. [Length: 70em]">
         To send net-export data, please configure your email account in the Settings app.
       </message>
@@ -1544,6 +1547,12 @@ While in incognito, sites can't use cookies to see your browsing activity across
       <message name="IDS_IOS_SCANNER_MULTIPLE_FOREGROUND_APPS_ALERT_TITLE" desc="Title of a modal dialog shown when the user tries to open the scanner in a Split View mode. [Length: 40em] [iOS only]" meaning="Title of a Split View error dialog in Scanner.">
         Split View
       </message>
+      <message name="IDS_IOS_SNACKBAR_MESSAGE_ICOGNITO_DISABLED" desc="The material toast message when incogonito mode is disabled by policy [iOS only].">
+        Your organization turned off incognito mode
+      </message>
+      <message name="IDS_IOS_SNACKBAR_MESSAGE_ICOGNITO_FORCED" desc="The material toast message when incogonito mode is forced by policy [iOS only].">
+        Your organization requires Incognito mode
+      </message>
       <message name="IDS_IOS_TOOLS_MENU_CELL_NEW_FEATURE_BADGE" desc="Title and accessibility label of the badge displayed on a tools menu item when it represents a new feature [Length: 20em]" meaning="A badge with this title is displayed informing the user that this feature that is new to them.">
         New
       </message>

ios/chrome/app/strings/ios_strings_grd/IDS_IOS_NAVIGATION_BAR_MORE_BUTTON.png.sha1

+015c671d78c341b546321cff853d75fecfa75b4a
\ No newline at end of file

ios/chrome/app/strings/ios_strings_grd/IDS_IOS_SNACKBAR_MESSAGE_ICOGNITO_DISABLED.png.sha1

+e2ad41fa47a46728dbdccf6d673cc4acbc28783a
\ No newline at end of file

ios/chrome/app/strings/ios_strings_grd/IDS_IOS_SNACKBAR_MESSAGE_ICOGNITO_FORCED.png.sha1

+afda53a7539958e42d7008e8979c18e060102763
\ No newline at end of file