[Picture in Picture] Only show controls when mouse is moving on Windows.

A previous change made controls always appear when the mouse is moving
on all OS except Windows. This change gates handling the ET_MOUSE_MOVED
event to Windows OS.

Bug: 870120
Change-Id: I556c354643a920c34b973066369e26f38130705f
Reviewed-on: https://chromium-review.googlesource.com/1161300
Commit-Queue: apacible <apacible@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580457}

chrome/browser/ui/views/overlay/overlay_window_views.cc

@@ -485,8 +485,10 @@ void OverlayWindowViews::OnMouseEvent(ui::MouseEvent* event) {
     // Only show the media controls when the mouse is hovering over the window.
     // This is checking for both ENTERED and MOVED because ENTERED is not fired
     // after a resize on Windows.
-    case ui::ET_MOUSE_ENTERED:
+#if defined (OS_WIN)
     case ui::ET_MOUSE_MOVED:
+#endif  // OS_WIN
+    case ui::ET_MOUSE_ENTERED:
       UpdateControlsVisibility(true);
       break;