Enable whole-program devirtualization for arm64 Android build.

Change-Id: I379eb250fd11836bb3b8584ce0235d782284e89f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2310327
Commit-Queue: Pavel Iliin <Pavel.Iliin@arm.com>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795521}

build/config/compiler/BUILD.gn

@@ -653,9 +653,9 @@ config("compiler") {
       }
     }
 
-    # TODO(pcc): Re-enable this flag on Android. This will require libc++ to be
-    # built with ThinLTO (see https://crbug.com/767901) as well as the GVR shim.
-    if (!is_android) {
+    # Whole-program devirtualization increases android libchrome.so size
+    # by ~100kb on arm32 and reduces it by ~108kb on arm64 instead.
+    if (!is_android || current_cpu == "arm64") {
       cflags += [ "-fwhole-program-vtables" ]
       if (!is_win) {
         ldflags += [ "-fwhole-program-vtables" ]