Use the host coordinate when comparing to host window bounds.

I somehow overlooked this and the test was not strict enough to catch this.

BUG=521919
TEST=Updated ScreenPositionControllerTest.ConvertHostPointToScreenHiDPI so that it fails without the patch.

Review URL: https://codereview.chromium.org/1293373002

Cr-Commit-Position: refs/heads/master@{#344186}
bool ShouldStayInSameRootWindow(const aura::Window* window) {
  return window && (window->GetProperty(kStayInSameRootWindowKey) ||
                    ShouldStayInSameRootWindow(window->parent()));
}

bool ShouldStayInSameRootWindow(const aura::Window* window) {
  return window && (window->GetProperty(kStayInSameRootWindowKey) ||
                    ShouldStayInSameRootWindow(window->parent()));
}
