Update QR Code scanner caption string and padding.

ios/chrome/app/strings/ios_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!--
 This file contains definition of resources that will be translated for each
 locale.  The strings in this file are specific to iOS.
 -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       output_all_resource_defines="false" source_lang_id="en" enc_check="möl">
   <outputs>
@@ skipping 1033 matching lines @@
       <message name="IDS_IOS_QR_SCANNER_TORCH_BUTTON_ACCESSIBILITY_LABEL" desc="Accessibility label for the button to turn torch on and off in the QR Scanner. The current state of the button is communicated using the accessibility value. [Length: unlimited] [iOS only]">
         Torch
       </message>
       <message name="IDS_IOS_QR_SCANNER_TORCH_OFF_ACCESSIBILITY_VALUE" desc="Accessiblity value of the button to turn torch on in the QR Scanner. The button communicates that the torch is current off. [Length: unlimited] [iOS only]">
         Off
       </message>
       <message name="IDS_IOS_QR_SCANNER_TORCH_ON_ACCESSIBILITY_VALUE" desc="Accessibility value of the button to turn torch off in the QR Scanner. The button communicates that the torch is currently on. [Length: unlimited] [iOS only]">
         On
       </message>
       <message name="IDS_IOS_QR_SCANNER_VIEWPORT_CAPTION" desc="Message displayed below the QR scanner viewport instructing the user to position the scanned QR or bar code inside the viewport. [Length: unlimited] [iOS only]">
-        QR Code or barcode
+        Position QR code or barcode in this frame
       </message>
       <message name="IDS_IOS_READING_LIST_SNACKBAR_MESSAGE" desc="Message briefly displayed at the bottom of the screen to the user to inform that the selected page has been added to the reading list. [Length: 35em]" meaning="The selected page has been added to your reading list. [Length: 35em]">
         Added to Reading List
       </message>
       <message name="IDS_IOS_READING_LIST_ENTRY_ACCESSIBILITY_LABEL" desc="Accessibility label for a reading list entry. Summarizes fields in the reading list entry (title, status and url). Read by Text To Speech.">
         <ph name="TITLE"><ex>Chromium - The Chromium Projects</ex>$1</ph>, <ph name="STATE"><ex>Available offline</ex>$2</ph>, <ph name="URL"><ex>http://www.chromium.org/Home</ex>$3</ph>
       </message>
       <message name="IDS_IOS_READING_LIST_ACCESSIBILITY_STATE_DOWNLOADED" desc="Accessibility label for the offline status of the reading list entry. Read by Text To Speech.">
         Available offline
       </message>
@@ skipping 489 matching lines @@
       </message>
       <message name="IDS_IOS_VOICE_SEARCH_SETTING_TITLE" desc="The title for Voice Search setting [Length: 29em] [iOS only]">
         Voice Search
       </message>
       <message name="IDS_IOS_VOICE_SEARCH_SETTING_TTS" desc="The label for setting switch enabling text-to-speech response after voice search [Length: 29em] [iOS only]">
         Speak Answers Back
       </message>
     </messages>
   </release>
 </grit>