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}
ScreenPositionController* GetScreenPositionController() {
  ShellTestApi test_api(Shell::GetInstance());
  return test_api.screen_position_controller();
}

ScreenPositionController* GetScreenPositionController() {
  ShellTestApi test_api(Shell::GetInstance());
  return test_api.screen_position_controller();
}
