Add partial magnifier to ash palette.

The partial magnifier will magnify a small portion of the screen, similar to a spyglass.

TEST=./out/Release/ash_unittests --gtest_filter=PartialMagnificationControllerTest.*
TBR=oshima@chromium.org

BUG=616112

Review-Url: https://codereview.chromium.org/2239553002
Cr-Commit-Position: refs/heads/master@{#414124}
app_list::AppListPresenter* ShellDelegateImpl::GetAppListPresenter() {
  if (!app_list_presenter_) {
    app_list_presenter_.reset(new app_list::AppListPresenterImpl(
        app_list_presenter_delegate_factory_.get()));
  }
  return app_list_presenter_.get();
}

app_list::AppListPresenter* ShellDelegateImpl::GetAppListPresenter() {
  if (!app_list_presenter_) {
    app_list_presenter_.reset(new app_list::AppListPresenterImpl(
        app_list_presenter_delegate_factory_.get()));
  }
  return app_list_presenter_.get();
}
