Building the Chromium-based WebView in AOSP is no longer supported. WebView can
now be built entirely from the Chromium source code.

General instructions for building WebView from Chromium:
https://www.chromium.org/developers/how-tos/build-instructions-android-webview

For questions about building WebView, please see
https://groups.google.com/a/chromium.org/forum/#!forum/android-webview-dev

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The prebuilt APKs here are built from Chromium upstream sources; check the
commit messages to see the version number for a particular prebuilt (the version
number looks like 74.0.3729.127 and this is also the name of the tag in the
Chromium git repository).

If you want to build your own WebView, you should build the latest stable
version, not the version published here: newer versions have important security
and stability improvements.

However, if you want to reproduce the native library (libwebviewchromium.so)
contained in these prebuilt APKs, you should be able to do so with the following
GN arguments:

target_os = "android"
is_debug = false
is_component_build = false
is_official_build = true
is_chrome_branded = false
use_official_google_api_keys = false
exclude_unwind_tables = true
ffmpeg_branding = "Chrome"
proprietary_codecs = true
enable_remoting = true

as well as specifying the appropriate target_cpu, which should be one of
"arm", "arm64", "x86" or "x64".

To build a complete WebView APK it is necessary to also set android_sdk_release
to the current Android SDK version (for example, "q"). However, it's not always
possible to do this successfully for all public Chromium versions: we are not
able to publish the required Java code changes to support a given Android
version until after that Android version's SDK has been publicly released, and
so the public versions of Chromium do not always support the latest version of
Android.