Start message loop on creation on Android

The message loop has to be started to post tasks on Android. Previously
the message loop is started on PreEarlyInitialization(). Now we need to
post tasks earlier than that. This change starts the message loop when
it being created on Android.

For files:
android_webview/browser/aw_browser_main_parts.cc,
chrome/browser/chrome_browser_main_android.cc,
chromecast/browser/cast_browser_main_parts.cc,
components/cronet/android/cronet_library_loader.cc,
content/shell/browser/shell_browser_main_parts.cc,
remoting/client/chromoting_client_runtime.cc

TBR=boliu@chromium.org,yfriedman@chromium.org,halliwell@chromium.org,kapishnikov@chromium.org,mkwst@chromium.org,garykac@chromium.org

Bug: 848615, 729596
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I4b2a2afb570096cc56339978ef8e4ba3f3f9ecc7
Reviewed-on: https://chromium-review.googlesource.com/1112958
Commit-Queue: Ran Ji <ranj@chromium.org>
Reviewed-by: Ran Ji <ranj@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573447}
17 files changed