Add timeline

Author: victorhuangwq

microsoft-edge/web-platform/site-impacting-changes.md

@@ -34,7 +34,7 @@ This table lists high-impact changes which the Microsoft Edge team is tracking c
 
 | Change | Release | Description |
 | --- | --- | --- |
-| Deprecate `getHostEnvironmentValue` | Future release (TBD) | Deprecate the non-standards-based, Microsoft Edge-only `window.external.getHostEnvironmentValue()` method, in favor of using the standardized User-Agent Client Hints API to expose browser and platform information.  User-Agent Client Hints provide browser and platform information in a more privacy-preserving way.  See [Detect Windows 11 and CPU architecture using User-Agent Client Hints](./how-to-detect-win11.md), and [User-Agent Client Hints API](https://developer.mozilla.org/docs/Web/API/User-Agent_Client_Hints_API). |
+| Deprecate `getHostEnvironmentValue` | v137-v141 | Deprecate the non-standards-based, Microsoft Edge-only `window.external.getHostEnvironmentValue()` method, in favor of using the standardized User-Agent Client Hints API to expose browser and platform information.  User-Agent Client Hints provide browser and platform information in a more privacy-preserving way.  See [Detect Windows 11 and CPU architecture using User-Agent Client Hints](./how-to-detect-win11.md), and [User-Agent Client Hints API](https://developer.mozilla.org/docs/Web/API/User-Agent_Client_Hints_API). |
 | Insecure downloads over HTTP | Future release (TBD) | When a user tries to download potentially dangerous content from an HTTP site, the user will receive a UI warning, such as "Insecure download blocked."  The user will still have an option to proceed and download the item.  Admins can use the `InsecureContentAllowedForUrls` policy to specify HTTP sites for which the warning will be suppressed.  Admins can use the `InsecureDownloadWarnings` feature flag to test the impact of this upcoming feature. |
 | Deprecate unload event | Future release (TBD) | Introduces a new Permission-Policy to allow creating unload event listeners. The default policy is `allow`, but the default policy will gradually be migrated to `deny`, such that unload handlers stop firing on pages, unless a page explicitly opts in to re-enable them.  This change is happening in the Chromium project, on which Microsoft Edge is based.  For more information, see [Intent to Deprecate: Deprecate unload event](https://groups.google.com/a/chromium.org/g/blink-dev/c/dvusqw9-IhI/m/SBkm_u1RAQAJ). |
 | Removal of cross-origin subframe JavaScript dialogs | Future release (TBD) | Removes `window.alert`, `window.prompt`, and `window.confirm` from cross-origin iframes.  This change is happening in the Chromium project, on which Microsoft Edge is based.  For more information, see [Intent to Remove: Cross origin subframe JS Dialogs](https://groups.google.com/a/chromium.org/g/blink-dev/c/hTOXiBj3D6A/m/JtkdpDd1BAAJ). |