feat: add new imageAnimationPolicy webpref and webContents setter (#29095)

docs/api/browser-window.md

@@ -294,6 +294,7 @@ It creates a new `BrowserWindow` with native properties as set by the `options`.
     * `allowRunningInsecureContent` Boolean (optional) - Allow an https page to run
       JavaScript, CSS or plugins from http URLs. Default is `false`.
     * `images` Boolean (optional) - Enables image support. Default is `true`.
+    * `imageAnimationPolicy` String (optional) - Specifies how to run image animations (E.g. GIFs).  Can be `animate`, `animateOnce` or `noAnimation`.  Default is `animate`.
     * `textAreasAreResizable` Boolean (optional) - Make TextArea elements resizable. Default
       is `true`.
     * `webgl` Boolean (optional) - Enables WebGL support. Default is `true`.

docs/api/web-contents.md

@@ -1923,6 +1923,20 @@ when the page becomes backgrounded. This also affects the Page Visibility API.
 
 Returns `String` - the type of the webContent. Can be `backgroundPage`, `window`, `browserView`, `remote`, `webview` or `offscreen`.
 
+#### `contents.setImageAnimationPolicy(policy)`
+
+* `policy` String - Can be `animate`, `animateOnce` or `noAnimation`.
+
+Sets the image animation policy for this webContents.  The policy only affects
+_new_ images, existing images that are currently being animated are unaffected.
+This is a known limitation in Chromium, you can force image animation to be
+recalculated with `img.src = img.src` which will result in no network traffic
+but will update the animation policy.
+
+This corresponds to the [animationPolicy][] accessibility feature in Chromium.
+
+[animationPolicy]: https://developer.chrome.com/docs/extensions/reference/accessibilityFeatures/#property-animationPolicy
+
 ### Instance Properties
 
 #### `contents.audioMuted`