Revert "[WebLayer] Remove support for M79"

This reverts commit 935efb98.

Reason for revert: As 81 hasn't shipped yet, and the client library is being used from trunk, this is a bit aggresive. We need to wait until 83 goes to stable before doing this.

Original change's description:
> [WebLayer] Remove support for M79
> 
> Fixes this TODO before M83 branches.
> 
> Bug: 1031830
> Change-Id: I280cc8378cb1124fdcc12965ff067382d669ef09
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2132827
> Auto-Submit: Clark DuVall <cduvall@chromium.org>
> Commit-Queue: Scott Violet <sky@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#755513}

TBR=sky@chromium.org,cduvall@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1031830
Change-Id: Ie53395a683e34b95750577cec2ccfab8141131f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2135539Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756258}

weblayer/public/java/org/chromium/weblayer/WebLayer.java

@@ -279,11 +279,14 @@ public class WebLayer {
                 }
                 Class factoryClass = remoteClassLoader.loadClass(
                         "org.chromium.weblayer_private.WebLayerFactoryImpl");
+                // NOTE: the 20 comes from the previous scheme of incrementing versioning. It must
+                // remain at 20 for Chrome version 79.
+                // TODO(https://crbug.com/1031830): change 20 to -1 when tip of tree is at 83.
                 mFactory = IWebLayerFactory.Stub.asInterface(
                         (IBinder) factoryClass
                                 .getMethod("create", String.class, int.class, int.class)
                                 .invoke(null, WebLayerClientVersionConstants.PRODUCT_VERSION,
-                                        WebLayerClientVersionConstants.PRODUCT_MAJOR_VERSION, -1));
+                                        WebLayerClientVersionConstants.PRODUCT_MAJOR_VERSION, 20));
                 available = mFactory.isClientSupported();
                 majorVersion = mFactory.getImplementationMajorVersion();
                 version = mFactory.getImplementationVersion();