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}
void WindowTreeHostManager::CloseMirroringDisplayIfNotNecessary() {
  mirror_window_controller_->CloseIfNotNecessary();
  if (!cursor_window_controller_->is_cursor_compositing_enabled())
    cursor_window_controller_->UpdateContainer();
}

void WindowTreeHostManager::CloseMirroringDisplayIfNotNecessary() {
  mirror_window_controller_->CloseIfNotNecessary();
  if (!cursor_window_controller_->is_cursor_compositing_enabled())
    cursor_window_controller_->UpdateContainer();
}
