Makes construction of (ash)RemoteWindowTreeHostWin explicit

ash/host/ash_remote_window_tree_host_win.cc

Index: ash/host/ash_remote_window_tree_host_win.cc
diff --git a/ash/host/ash_remote_window_tree_host_win.cc b/ash/host/ash_remote_window_tree_host_win.cc
index ff8c8df5b5c82881421aae62a1798d8b2cea2603..67d3aaa8862f12c77251d2b37ce7775379a7c9a0 100644
--- a/ash/host/ash_remote_window_tree_host_win.cc
+++ b/ash/host/ash_remote_window_tree_host_win.cc
@@ -9,32 +9,14 @@
 #include "ui/gfx/transform.h"
 
 namespace ash {
-namespace {
-AshRemoteWindowTreeHostWin* g_instance = NULL;
-}
-
-// static
-void AshRemoteWindowTreeHostWin::Init() {
-  DCHECK(!g_instance);
-  g_instance = new AshRemoteWindowTreeHostWin();
-  aura::RemoteWindowTreeHostWin::SetInstance(g_instance);
-  CHECK_EQ(g_instance, aura::RemoteWindowTreeHostWin::Instance());
-}
-
-// static
-AshRemoteWindowTreeHostWin* AshRemoteWindowTreeHostWin::GetInstance() {
-  if (!g_instance)
-    Init();
-  CHECK_EQ(g_instance, aura::RemoteWindowTreeHostWin::Instance());
-  return g_instance;
-}
 
-AshRemoteWindowTreeHostWin::AshRemoteWindowTreeHostWin()
-    : aura::RemoteWindowTreeHostWin(gfx::Rect()), transformer_helper_(this) {
-  g_instance = this;
+AshRemoteWindowTreeHostWin::AshRemoteWindowTreeHostWin(HWND remote_hwnd)
+    : aura::RemoteWindowTreeHostWin(),
+      transformer_helper_(this) {
+  SetRemoteWindowHandle(remote_hwnd);
 }
 
-AshRemoteWindowTreeHostWin::~AshRemoteWindowTreeHostWin() { g_instance = NULL; }
+AshRemoteWindowTreeHostWin::~AshRemoteWindowTreeHostWin() {}
 
 void AshRemoteWindowTreeHostWin::ToggleFullScreen() {}