Revert of Disable Mojo on RenderThreadImplBrowserTest on Android (patchset #1...

Revert of Disable Mojo on RenderThreadImplBrowserTest on Android (patchset #1 id:1 of https://codereview.chromium.org/866973004/)

Reason for revert:
This doesn't work in some tests.

Original issue's description:
> Disable Mojo on RenderThreadImplBrowserTest on Android
>
> It hasn't worked from the beginning and it blocks ChannelMojo from
> being enabled.
>
> BUG=451221
> R=jcivelli@chromium.org, sky@chromium.org
>
> Committed: https://crrev.com/b5a99f2c1652471236c5d07403faa42bf53420df
> Cr-Commit-Position: refs/heads/master@{#312875}

TBR=jcivelli@chromium.org,sky@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=451221

Review URL: https://codereview.chromium.org/873913002

Cr-Commit-Position: refs/heads/master@{#312988}

content/test/render_thread_impl_browser_test_ipc_helper.cc

@@ -23,18 +23,7 @@ RenderThreadImplBrowserIPCTestHelper::RenderThreadImplBrowserIPCTestHelper() {
 
   SetupIpcThread();
 
-  // TODO(crbug.com/451221): Mojo should be used here even for Android.
-  // Currently SetupMojo() calls InitializeMojo() which can be called at most
-  // once for each process. This implices that every test case using
-  // RenderThreadImplBrowserIPCTestHelper has to run in a dedicated process, but
-  // that is false on OS_ANDROID. There is no way to call InitializeMojo() only
-  // if it isn't initialized yet.
-#if defined(OS_ANDROID)
-  bool use_mojo_channel = false;
-#else
-  bool use_mojo_channel = IPC::ChannelMojo::ShouldBeUsed();
-#endif
-  if (use_mojo_channel) {
+  if (IPC::ChannelMojo::ShouldBeUsed()) {
     SetupMojo();
   } else {
     channel_ = IPC::ChannelProxy::Create(channel_id_, IPC::Channel::MODE_SERVER,