Enable multidex on components_browsertests

Dex limit is being reached on some builders.

TBR=sdefresne@chromium.org

Bug: 807936
Change-Id: Ic8bcff99759ebb348ae336489ab52ca921b6d958
Reviewed-on: https://chromium-review.googlesource.com/897808Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533669}

components/BUILD.gn

@@ -488,6 +488,7 @@ if (!is_ios) {
     }
 
     if (is_android) {
+      enable_multidex = true
       sources += [
         "test/android/browsertests_apk/components_browser_tests_jni_onload.cc",
       ]