[WebLayer] Enable WebLayer in split on dev/beta

There hasn't been any spikes in crashes in canary, so should be safe to
move this to dev/beta.

Bug: 1105096
Change-Id: I584c882013ed7f20b03461a654250d955253f2d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2426145Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809996}

weblayer/variables.gni

@@ -9,8 +9,7 @@ declare_args() {
   webview_includes_weblayer = true
 
   # Whether WebLayer will be included as a DFM.
-  weblayer_in_split =
-      android_channel == "default" || android_channel == "canary"
+  weblayer_in_split = android_channel != "stable"
 }
 
 weblayer_product_config_java_package = "org.chromium.weblayer_private"