docs: Add docs for 1.49.0's new "chromium" option

Reword channel documentation - as someone unfamiliar with the differences in Playwright's use of Chromium versus Google Chrome, I found the 1.49.0 release notes confusing. This may help.

Update browsers.md list of channels to match params.md.

docs/src/api/params.md

@@ -1001,7 +1001,11 @@ Additional arguments to pass to the browser instance. The list of Chromium flags
 ## browser-option-channel
 - `channel` <[string]>
 
-Browser distribution channel.  Supported values are "chrome", "chrome-beta", "chrome-dev", "chrome-canary", "msedge", "msedge-beta", "msedge-dev", "msedge-canary". Read more about using [Google Chrome and Microsoft Edge](../browsers.md#google-chrome--microsoft-edge).
+Browser distribution channel.
+
+Use "chromium" to [opt in to new headless mode](../browsers.md#opt-in-to-new-headless-mode).
+
+Use "chrome", "chrome-beta", "chrome-dev", "chrome-canary", "msedge", "msedge-beta", "msedge-dev", or "msedge-canary" to use branded [Google Chrome and Microsoft Edge](../browsers.md#google-chrome--microsoft-edge).
 
 ## browser-option-chromiumsandbox
 - `chromiumSandbox` <[boolean]>

docs/src/browsers.md

@@ -423,7 +423,7 @@ dotnet test -- Playwright.BrowserName=chromium Playwright.LaunchOptions.Channel=
 
 While Playwright can download and use the recent Chromium build, it can operate against the branded Google Chrome and Microsoft Edge browsers available on the machine (note that Playwright doesn't install them by default). In particular, the current Playwright version will support Stable and Beta channels of these browsers.
 
-Available channels are `chrome`, `msedge`, `chrome-beta`, `msedge-beta` or `msedge-dev`.
+Available channels are `chrome`, `msedge`, `chrome-beta`, `msedge-beta`, `chrome-dev`, `msedge-dev`, `chrome-canary`, `msedge-canary`.
 
 :::warning
 Certain Enterprise Browser Policies may impact Playwright's ability to launch and control Google Chrome and Microsoft Edge. Running in an environment with browser policies is outside of the Playwright project's scope.

packages/playwright-core/types/types.d.ts

@@ -14709,9 +14709,12 @@ export interface BrowserType<Unused = {}> {
     bypassCSP?: boolean;
 
     /**
-     * Browser distribution channel.  Supported values are "chrome", "chrome-beta", "chrome-dev", "chrome-canary",
+     * Browser distribution channel.
-     * "msedge", "msedge-beta", "msedge-dev", "msedge-canary". Read more about using
+     *
-     * [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
+     * Use "chromium" to [opt in to new headless mode](https://playwright.dev/docs/browsers#opt-in-to-new-headless-mode).
+     *
+     * Use "chrome", "chrome-beta", "chrome-dev", "chrome-canary", "msedge", "msedge-beta", "msedge-dev", or
+     * "msedge-canary" to use branded [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
      */
     channel?: string;
 
@@ -15205,9 +15208,12 @@ export interface BrowserType<Unused = {}> {
     args?: Array<string>;
 
     /**
-     * Browser distribution channel.  Supported values are "chrome", "chrome-beta", "chrome-dev", "chrome-canary",
+     * Browser distribution channel.
-     * "msedge", "msedge-beta", "msedge-dev", "msedge-canary". Read more about using
+     *
-     * [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
+     * Use "chromium" to [opt in to new headless mode](https://playwright.dev/docs/browsers#opt-in-to-new-headless-mode).
+     *
+     * Use "chrome", "chrome-beta", "chrome-dev", "chrome-canary", "msedge", "msedge-beta", "msedge-dev", or
+     * "msedge-canary" to use branded [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
      */
     channel?: string;
 
@@ -21540,9 +21546,12 @@ export interface LaunchOptions {
   args?: Array<string>;
 
   /**
-   * Browser distribution channel.  Supported values are "chrome", "chrome-beta", "chrome-dev", "chrome-canary",
+   * Browser distribution channel.
-   * "msedge", "msedge-beta", "msedge-dev", "msedge-canary". Read more about using
+   *
-   * [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
+   * Use "chromium" to [opt in to new headless mode](https://playwright.dev/docs/browsers#opt-in-to-new-headless-mode).
+   *
+   * Use "chrome", "chrome-beta", "chrome-dev", "chrome-canary", "msedge", "msedge-beta", "msedge-dev", or
+   * "msedge-canary" to use branded [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
    */
   channel?: string;
 

packages/playwright/types/test.d.ts

@@ -5776,9 +5776,12 @@ export interface PlaywrightWorkerOptions {
    */
   headless: boolean;
   /**
-   * Browser distribution channel.  Supported values are "chrome", "chrome-beta", "chrome-dev", "chrome-canary",
+   * Browser distribution channel.
-   * "msedge", "msedge-beta", "msedge-dev", "msedge-canary". Read more about using
+   *
-   * [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
+   * Use "chromium" to [opt in to new headless mode](https://playwright.dev/docs/browsers#opt-in-to-new-headless-mode).
+   *
+   * Use "chrome", "chrome-beta", "chrome-dev", "chrome-canary", "msedge", "msedge-beta", "msedge-dev", or
+   * "msedge-canary" to use branded [Google Chrome and Microsoft Edge](https://playwright.dev/docs/browsers#google-chrome--microsoft-edge).
    *
    * **Usage**
    *