Screen curtain does not actually save on battery life in iOS, as the screen is technically still on. It does, however, provide privacy. So, maybe a hotkey to turn off the screen completely would be nice... not sure.

The workaround of setting screen brightness works until next key-press, and then brightness goes to 6%.

David, is this something you could take on in the coming milestones as part of our phase 4 work? Or if you'd like me to try to find someone outside of our team to dig into this, let me know. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3a17f21225fc435f31e588292073eab3e4952502

commit 3a17f21225fc435f31e588292073eab3e4952502
Author: dtseng <dtseng@chromium.org>
Date: Sat Mar 25 08:58:52 2017

Wire up an api to darken screen for accessibility

BUG= 625741 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2768703002
Cr-Commit-Position: refs/heads/master@{#459646}

[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/accessibility/accessibility_extension_api.cc
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/accessibility/accessibility_extension_api.h
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/chromeos/accessibility/accessibility_manager.cc
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/BUILD.gn
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/chromevox/background/externs.js
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/chromevox/background/keymaps/next_keymap.json
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/chromevox/background/tabs_api_handler.js
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[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/cvox2/background/background.js
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[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/cvox2/background/output.js
[delete] https://crrev.com/fd745bdf5030fdab0ae54eb87c784b161206cd33/chrome/browser/resources/chromeos/chromevox/cvox2/background/stubs.js
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/strings/chromevox_strings.grd
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/browser/resources/chromeos/chromevox/tools/check_chromevox.py
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/chrome/common/extensions/api/accessibility_private.json
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/extensions/browser/extension_function_histogram_value.h
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/third_party/closure_compiler/externs/accessibility_private.js
[modify] https://crrev.com/3a17f21225fc435f31e588292073eab3e4952502/tools/metrics/histograms/histograms.xml