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 HandleTakeScreenshot(ScreenshotDelegate* screenshot_delegate) {
  base::RecordAction(UserMetricsAction("Accel_Take_Screenshot"));
  DCHECK(screenshot_delegate);
  if (screenshot_delegate->CanTakeScreenshot())
    screenshot_delegate->HandleTakeScreenshotForAllRootWindows();
}

void HandleTakeScreenshot(ScreenshotDelegate* screenshot_delegate) {
  base::RecordAction(UserMetricsAction("Accel_Take_Screenshot"));
  DCHECK(screenshot_delegate);
  if (screenshot_delegate->CanTakeScreenshot())
    screenshot_delegate->HandleTakeScreenshotForAllRootWindows();
}
