Update WebView prerelease docs for Trichrome.

Include details about how to use TrichromeWebView prerelease channels in
the documentation.

Bug: 1016502
Change-Id: Ifb7b8878f6a85d57e01a637922036f8870923d48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929519
Commit-Queue: Richard Coles <torne@chromium.org>
Auto-Submit: Richard Coles <torne@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718322}

android_webview/docs/channels.md

@@ -76,11 +76,6 @@ the installed versions of Chrome to use as the WebView.
 
 ## Trichrome (Android Q+)
 
-*** promo
-The channels described in the following section are not yet available via the
-Play Store, but will be by the date of release of Android Q.
-***
-
 For Android Q+, WebView and Chrome are again separately installed APKs. However,
 Google began building a separate package of WebView for each of the four Chrome
 channels: Stable, Beta, Dev, and Canary. Like with Monochrome, users can find

android_webview/docs/faq.md

@@ -32,6 +32,10 @@ They still don’t share any data, however, and you can disable Google Chrome at
 any time without impairing your device. When Chrome is disabled, WebView will
 switch to a standalone version which isn't combined with Chrome.
 
+In Android 10 (Q), WebView and Chrome still share most of their code to save
+space and memory on your device, but now simply appear as two separate apps and
+there is no longer any special behaviour when disabling Chrome.
+
 ## Are Chrome features like Sync or Data Saver available in WebView?
 
 No. Although WebView and Chrome share a package in Android N, O, and P, they

android_webview/docs/prerelease.md

@@ -45,10 +45,39 @@ version of WebView around.
 
 Steps depend on your version of Android:
 
+### Android 10 (Q)
+
+Pre-release channels must be downloaded and installed as separate apps, but only
+one must be chosen to provide the system's WebView implementation at any given
+time.
+
+*** note
+WebView pre-release channels are independent of Chrome in Android 10 and later.
+Chrome can no longer be used as a WebView implementation in Android 10.
+***
+
+1. Download a pre-release channel of WebView from the play store, available here:
+   - [WebView Beta](https://play.google.com/store/apps/details?id=com.google.android.webview.beta)
+   - [WebView Dev](https://play.google.com/store/apps/details?id=com.google.android.webview.dev)
+   - [WebView Canary](https://play.google.com/store/apps/details?id=com.google.android.webview.canary)
+2. Follow the [steps to enable Android's developer options
+   menu](https://developer.android.com/studio/debug/dev-options)
+3. Choose Developer Options > WebView implementation (see figure)
+
+   ![The "WebView implementation" menu](/android_webview/docs/images/webview_implementations_menu_10.png)
+
+4. Choose the channel that you would like to use for WebView
+
+#### Returning to stable WebView
+
+1. To return to WebView stable, select "Android System WebView" again in the
+   WebView implementation menu
+
 ### Android 7 through 9 (Nougat/Oreo/Pie)
 
-Pre-release channels must be downloaded and installed as separate apps, but one
-must be chosen to provide the system's WebView implementation at any given time.
+Pre-release channels must be downloaded and installed as separate apps, but only
+one must be chosen to provide the system's WebView implementation at any given
+time.
 
 1. Download a pre-release channel of Chrome from the play store, available here:
    - [Chrome Beta](https://play.google.com/store/apps/details?id=com.chrome.beta)
@@ -113,12 +142,16 @@ adb shell cmd webviewupdate set-webview-implementation <packagename>
 
 Package names are as follows:
 
-|App name                |Package name                            |
-|-----------------------:|----------------------------------------|
-|Chrome (stable)         |com.android.chrome                      |
-|Chrome Beta             |com.chrome.beta                         |
-|Chrome Dev              |com.chrome.dev                          |
-|Chrome Canary           |com.chrome.canary                       |
+|App name                    |Package name                            |
+|---------------------------:|----------------------------------------|
+|Chrome (stable, 7/8/9 only) |com.android.chrome                      |
+|Chrome Beta (7/8/9 only)    |com.chrome.beta                         |
+|Chrome Dev (7/8/9 only)     |com.chrome.dev                          |
+|Chrome Canary (7/8/9 only)  |com.chrome.canary                       |
+|WebView (stable)            |com.google.android.webview              |
+|WebView Beta (10+ only)     |com.google.android.webview.beta         |
+|WebView Dev (10+ only)      |com.google.android.webview.dev          |
+|WebView Canary (10+ only)   |com.google.android.webview.canary       |
 
 ## See also
 - [WebView channels in detail](/android_webview/docs/channels.md)