Document pixel dimension limit for WallpaperImage policy.

components/policy/resources/policy_templates.json

 {
 # policy_templates.json - Metafile for policy templates
 #
 # The content of this file is evaluated as a Python expression.
 #
 # This file is used as input to generate the following policy templates:
 # ADM, ADMX+ADML, MCX/plist and html documentation.
 #
 # Policy templates are user interface definitions or documents about the
 # policies that can be used to configure Chrome. Each policy is a name-value
@@ skipping 6491 matching lines @@
       'features': {
         'dynamic_refresh': True,
         'per_profile': True,
       },
       'example_value': { "url": "http://example.com/wallpaper.jpg", "hash": "baddecafbaddecafbaddecafbaddecafbaddecafbaddecafbaddecafbaddecaf" },
       'max_size': 16777216,
       'id': 262,
       'caption': '''Wallpaper image''',
       'desc': '''Configure wallpaper image.
 
-      This policy allows you to configure the wallpaper image that is shown on the desktop and on the login screen background for the user. The policy is set by specifying the URL from which <ph name="PRODUCT_OS_NAME">$2<ex>Google Chrome OS</ex></ph> can download the wallpaper image and a cryptographic hash used to verify the integrity of the download. The image must be in JPEG format, its size must not exceed 16MB. The URL must be accessible without any authentication.
+      This policy allows you to configure the wallpaper image that is shown on the desktop and on the login screen background for the user. The policy is set by specifying the URL from which <ph name="PRODUCT_OS_NAME">$2<ex>Google Chrome OS</ex></ph> can download the wallpaper image and a cryptographic hash used to verify the integrity of the download. The image must be in JPEG format, its file size must not exceed 16MB and its dimension must not exceed 32 megapixels. The URL must be accessible without any authentication.
 
       The wallpaper image is downloaded and cached. It will be re-downloaded whenever the URL or the hash changes.
 
       The policy should be specified as a string that expresses the URL and hash in JSON format, conforming to the following schema:
       {
         "type": "object",
         "properties": {
           "url": {
             "description": "The URL from which the wallpaper image can be downloaded.",
             "type": "string"
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       'desc': '''Text appended in parentheses to the policy name to indicate that it has been deprecated''',
       'text': 'deprecated',
     },
     'doc_recommended': {
       'desc': '''Text appended in parentheses next to the policies top-level container to indicate that those policies are of the Recommended level''',
       'text': 'Default Settings (users can override)',
     },
   },
   'placeholders': [],
 }