Since the introduction of WebView as an updatable APK in Android L, WebView has had some conception of pre-release channels. The details of the implementation of these channels has differed between different generations of WebView, and this document explains those details.
The pre-release channels strategy of Chrome for Android has been to build separate APKs, each with a unique package name, so that they can be installed side-by-side. In contrast, Standalone WebView has only a single package name (com.google.android.webview) that is recognized by Android as a valid WebView provider, and instead utilizes the “tracks” API provided by Google Play. This allows users to opt-in to beta updates, but users cannot have simultaneous installations of both stable and beta Standalone WebView on a single device.
All users that have Android System WebView installed and enabled are eligible to receive updates published to the production track. In addition, users can opt-in to the beta track by joining the beta tester program. Once a user's account is in the beta program, it is eligible to receive updates that have been published to the beta track. The Play Store updates users to the APK with the highest versionCode among eligible tracks.
Google publishes an APK of Android System WebView to the beta track based on the same release cycle as Chrome Beta.
Similarly, builds of Chrome for “Dev” channel releases include a build of WebView which gets published to an alpha track. Only users belonging to specific internal Google groups are eligible for Play Store updates from Android System WebView alpha track, including members of Google's internal Chrome for Android and Android WebView teams.
Prior to version 75, WebView's internal logic had no way of knowing whether it had been built for a dev, beta, or stable release. Beginning with version 75.0.3770.40, Google builds separate APKs for each of stable, beta, and dev channels, with the internal logic differing only in that it is aware of which channel it was built for.
This change allows for different logic flow depending on the channel, such as sampling crash reports differently, targeting beta users for experiments, etc.
With this change, the WebView APKs belonging to the three different channels were given unique versionCode values, with stable having a final digit of 0, beta a final digit of 1, and dev 2. Having identical package names required unique versionCodes for the different channel builds to exist simultaneously on platforms like Google Play and Google's internal crash and performance analytics infrastructure. These specific values were chosen so that a user who has opted into the beta program will still receive the beta APK (Play Store delivers the APK with the higher versionCode value) even if a stable APK from the same build is available (such as when we promote a beta build to stable), so that the user can receive beta-targeted experiments.
To avoid conflicting with Trichrome WebView's pre-release channel strategy, Standalone WebView APKs are given a maxSdkVersion value of 28, so that users who have opted into the beta program described above do not experience the Play Store updating their Trichrome WebView stable APK to Standalone WebView beta (since they share the same package name).
For Android versions N - P, WebView is built as a part of the Chrome APK. Since Chrome already supported side-by-side installs of different Chrome channels on Android, a menu was added to Android's Developer Options Settings that allows a user to choose which of the installed versions of Chrome to use as the WebView.
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 each of these four channels of WebView on the Play Store and install them simultaneously on a single device. Also like Monochrome, users can use the “WebView implementation” menu to choose which installed WebView the system should use.
Trichrome WebView APKs (of all channels) have a versionCode value with a final digit of 3 (to match Trichrome Chrome's versionCode).
Users may choose to opt into the beta program for Android System WebView (com.google.android.webview), but it will have no effect on Android Q, as the only APK of this package that gets published to the beta track is Standalone WebView, which has a maxSdkVersion value of 28. While confusing, this helps avoid the user's stable WebView installation being updated to beta, since the preferred method for using WebView beta on Android Q is installing the separate package from the Play Store. Without this, the same package would receive updates from the builds of both Trichrome WebView stable (at the time of a stable release) and Standalone WebView beta (at the time of a beta promotion). Switching back and forth between these generations would involve very large update deltas.
