Fix WebLayer loading with isolated splits in Monochrome

WebLayer needs its base_module_java to be in the base module to load
correctly.

Bug: 1126301
Change-Id: I0dc89a897922c33695e8e0ede4be8b849ae7dffc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487821
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819036}

chrome/android/BUILD.gn

@@ -2078,6 +2078,9 @@ android_library("base_monochrome_module_java") {
     "//chrome/browser/version:java",
     "//components/version_info/android:version_constants_java",
   ]
+  if (webview_includes_weblayer) {
+    deps += [ "//weblayer/browser/java:base_module_java" ]
+  }
 }
 
 # Target for classes which should be in the base module, even when