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 PaletteDelegateChromeOS::TakePartialScreenshot() {
  auto* screenshot_controller =
      ash::Shell::GetInstance()->screenshot_controller();
  auto* screenshot_delegate = ash::Shell::GetInstance()
                                  ->accelerator_controller_delegate()
                                  ->screenshot_delegate();

  screenshot_controller->set_pen_events_only(true);
  screenshot_controller->StartPartialScreenshotSession(
      screenshot_delegate, false /* draw_overlay_immediately */);
}

void PaletteDelegateChromeOS::TakePartialScreenshot() {
  auto* screenshot_controller =
      ash::Shell::GetInstance()->screenshot_controller();
  auto* screenshot_delegate = ash::Shell::GetInstance()
                                  ->accelerator_controller_delegate()
                                  ->screenshot_delegate();

  screenshot_controller->set_pen_events_only(true);
  screenshot_controller->StartPartialScreenshotSession(
      screenshot_delegate, false /* draw_overlay_immediately */);
}
