Based on your comments in https://codereview.webrtc.org/2496413002#msg16, it sounds like this might be as simple as some translation logic gated behind a conditional that checks for kFullDesktopScreenId. I can certainly throw up a quick CL to do that.

The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/31bbee73a029376ca5a6f74e3d5bf224053a6208

commit 31bbee73a029376ca5a6f74e3d5bf224053a6208
Author: erikchen <erikchen@chromium.org>
Date: Thu Mar 09 21:19:03 2017

mac: Fix screen capture for whole-desktop capture.

DisplayStream refresh rects are in display coordinates. When the whole screen is
being captured, the coordinates passed to the ScreenCapturerHelper need to be in
screen coordinates. This CL translates display coordinates to screen
coordinates for whole screen capture.

BUG= chromium:699672 

Review-Url: https://codereview.webrtc.org/2740823002
Cr-Commit-Position: refs/heads/master@{#17153}

[modify] https://crrev.com/31bbee73a029376ca5a6f74e3d5bf224053a6208/webrtc/modules/desktop_capture/screen_capturer_mac.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/31bbee73a029376ca5a6f74e3d5bf224053a6208

commit 31bbee73a029376ca5a6f74e3d5bf224053a6208
Author: erikchen <erikchen@chromium.org>
Date: Thu Mar 09 21:19:03 2017

mac: Fix screen capture for whole-desktop capture.

DisplayStream refresh rects are in display coordinates. When the whole screen is
being captured, the coordinates passed to the ScreenCapturerHelper need to be in
screen coordinates. This CL translates display coordinates to screen
coordinates for whole screen capture.

BUG= chromium:699672 

Review-Url: https://codereview.webrtc.org/2740823002
Cr-Commit-Position: refs/heads/master@{#17153}

[modify] https://crrev.com/31bbee73a029376ca5a6f74e3d5bf224053a6208/webrtc/modules/desktop_capture/screen_capturer_mac.mm

I'm not familiar with merging webrtc changes to branches - can someone take care of that part?

Your change meets the bar and is auto-approved for M58. Please go ahead and merge the CL to branch 3029 manually. Please contact milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), bhthompson@(cros), govind@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Please merge your change to M58 branch 3029 before 5:00 PM PT, Monday (03/13/17) so we can take it in for next week dev release. Thank you!

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

If all merges have been completed, please remove any remaining Merge-Approved labels from this issue.

Thanks for your time! To disable nags, add the Disable-Nags label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Your change is approved for M58. Please ensure whether this fix is verified in canary. If yes, please merge ASAP so that it will be picked up for Beta promotion RC cut on 03/15 at 5.00 PM PST.

The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/5810d27a9b13fe581282acc33350525be43e6f95

commit 5810d27a9b13fe581282acc33350525be43e6f95
Author: Sergey Ulanov <sergeyu@chromium.org>
Date: Wed Mar 15 18:40:11 2017

mac: Fix screen capture for whole-desktop capture.

DisplayStream refresh rects are in display coordinates. When the whole screen is
being captured, the coordinates passed to the ScreenCapturerHelper need to be in
screen coordinates. This CL translates display coordinates to screen
coordinates for whole screen capture.

BUG= chromium:699672 

Review-Url: https://codereview.webrtc.org/2740823002
Cr-Commit-Position: refs/heads/master@{#17153}
(cherry picked from commit 31bbee73a029376ca5a6f74e3d5bf224053a6208)

Review-Url: https://codereview.webrtc.org/2755663004 .
Cr-Commit-Position: refs/branch-heads/58@{#4}
Cr-Branched-From: f31969a584bcafe9406c214a9d4c3afb49d19650-refs/heads/master@{#16937}

[modify] https://crrev.com/5810d27a9b13fe581282acc33350525be43e6f95/webrtc/modules/desktop_capture/screen_capturer_mac.mm

Per comment #11, this is already merged to M58. Hence, removing "Merge-Approved-58" label. 

When connecting to a Mac mini with two equal sized monitors, this is fixed. The mini is non-corp. When connecting to a corp MBP with a second monitor connected through Displayport with curtain mode on, one screen is fine but the other is black. I do not have access to another corp Mac, so cannot say if this is because the second monitor is not the same resolution, if its because its corp, or if its because curtain mode is on. I'll disable curtain mode and update the bug with the results. 

When connecting to the MBP with curtain mode off, both displays show up, so it is mostly correct. However, there is corruption below the area of the first monitor (the smaller one) which fills in the gap to match the size of the second monitor. 

AJ, can you please attach a screenshot?

After connecting from a different client, I can no longer repro what I described above. Instead, the client only shows the primary monitor. I wrote  bug 704781  for this. 

Verified Fixed in 58.0.3029.28