Android: Enable vertical class merging in R8

Bug: 1040534
Change-Id: Ic9873612462612e510b91d713c24c046e017cafb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368510
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801359}

build/android/gyp/proguard.py

@@ -253,6 +253,7 @@ def _OptimizeWithR8(options,
 
     cmd = build_utils.JavaCmd(options.warnings_as_errors) + [
         '-Dcom.android.tools.r8.allowTestProguardOptions=1',
+        '-Dcom.android.tools.r8.enableVerticalClassMerging=1',
     ]
     if options.disable_outlining:
       cmd += ['-Dcom.android.tools.r8.disableOutlining=1']