Reland of Android: support multiple displays on C++ side

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index 648873d6c243ff38638dfb43e33d088dd150381f..d35871c41ae018fe0b44c6bf88489b504713329e 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -121,6 +121,8 @@
 #include "content/public/browser/screen_orientation_provider.h"
 #include "gpu/ipc/client/android/in_process_surface_texture_manager.h"
 #include "media/base/android/media_client_android.h"
+#include "ui/android/screen_android.h"
+#include "ui/display/screen.h"
 #include "ui/gl/gl_surface.h"
 #endif
 
@@ -735,6 +737,11 @@ void BrowserMainLoop::PostMainMessageLoopStart() {
 }
 
 int BrowserMainLoop::PreCreateThreads() {
+#if defined(OS_ANDROID)
+  // Let screen instance be overridable by parts.
+  display::Screen::SetScreenInstance(ui::CreateScreenAndroid());

[boliu, 2016/11/11 19:54:48]

linux puts this in PreMainMessageLoopRun

[Tima Vaisburd, 2016/11/11 21:32:25]

Sometimes it is in PreCreateThreads, though under USE_AURA:

https://cs.chromium.org/chromium/src/chrome/browser/ui/views/chrome_browser_m...
https://cs.chromium.org/chromium/src/chromecast/browser/cast_browser_main_par...

I moved, assuming USE_AURA and OS_ANDROID are mutually exclusive and I won't
override the existing setting. However, doesn't PreCreateThreads feel safer?

[boliu, 2016/11/11 21:36:10]

it hurts start up perf more

[Tima Vaisburd, 2016/11/11 23:44:43]

Done.
The relevant tests seem to pass again.

+#endif
+
   if (parts_) {
     TRACE_EVENT0("startup",
         "BrowserMainLoop::CreateThreads:PreCreateThreads");