[Desktop Android CRX] Fix test failure due to enabling extensions

We are experimenting with desktop-android configurations for Chrome.

This change addresses a crash occurring in AndroidBrowserTests (e.g.,
`PasswordAutofillAgentTest`) that utilize `ChromeRenderViewTest::SetUp`. The issue stems from
`ChromeRenderViewTest::InitChromeContentRendererClient()` not enabling
the necessary extensions code path, which prevents proper creation and setup of the ChromeExtensionsRendererClient, leading to a null `dispatcher_` and subsequent crashes in `ExtensionsRendererClient::RenderFrameCreated()`.

By ensuring the extensions code path is correctly enabled, this cl
fixes at least 191 test cases in android_browsertests.

This CL affects only tests, should have no behavior change.

Bug: 356905053
Change-Id: I7e7ff3b7214de4e04ece655337583b5ff526eb78
Cq-Include-Trybots: luci.chromium.try:android-desktop-14-x64-rel,android-desktop-x64-compile-rel,android-desktop-arm64-compile-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5904726
Commit-Queue: Jenny Zhang <jennyz@chromium.org>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1363314}