Taking a look.  Interestingly, I'm seeing an apparent freeze when I try to exit webvr.

I'm not seeing this repro, so resolving "won't fix" - the content size (both quad, and apparent resolution/scaling) seem equivalent whether I enter webvr then exit presentation, or get to the site by navigating in vr.

Saw this.  went to a webvr site, hit the app button to exit presentation, and then navigated back to the webvr samples page.  Scaling was off.

My repro:
1. went to webvr.info's sample page
2. navigated to the presentation sample
3. clicked "enter vr" to start presentation
4. hit the app button on the controller
5. navigated back while still in vr browsing

expected: correctly sized readable text.
actual: the entire page was scaled down so text was unreadable

It looks like app button click (and exiting WebVR through exit present) don't setContentCssSize, and they should.  Sent out a cr.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/625bfbd862c294832d217c35245e7b61a1e6ccfb

commit 625bfbd862c294832d217c35245e7b61a1e6ccfb
Author: billorr <billorr@chromium.org>
Date: Wed May 31 22:48:15 2017

VR: Content size incorrect when transitioning from webVR into VR Shell

The issue here is we are setting the virtual display's size when we
enter WebVR, but not when we exit it to VrShell.  This means that
content is incorrectly sized.

The fix simply sets the virtual display's size when we exit WebVR to VrShell.

BUG= 718578 

Review-Url: https://codereview.chromium.org/2906173002
Cr-Commit-Position: refs/heads/master@{#476074}

[modify] https://crrev.com/625bfbd862c294832d217c35245e7b61a1e6ccfb/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/625bfbd862c294832d217c35245e7b61a1e6ccfb

commit 625bfbd862c294832d217c35245e7b61a1e6ccfb
Author: billorr <billorr@chromium.org>
Date: Wed May 31 22:48:15 2017

VR: Content size incorrect when transitioning from webVR into VR Shell

The issue here is we are setting the virtual display's size when we
enter WebVR, but not when we exit it to VrShell.  This means that
content is incorrectly sized.

The fix simply sets the virtual display's size when we exit WebVR to VrShell.

BUG= 718578 

Review-Url: https://codereview.chromium.org/2906173002
Cr-Commit-Position: refs/heads/master@{#476074}

[modify] https://crrev.com/625bfbd862c294832d217c35245e7b61a1e6ccfb/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java

Your change meets the bar and is auto-approved for M60. Please go ahead and merge the CL to branch 3112 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), josafat@(ChromeOS), bustamante@(Desktop)

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

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/079395cb4a1ae3e6267aada372111300602ceb2e

commit 079395cb4a1ae3e6267aada372111300602ceb2e
Author: billorr <billorr@chromium.org>
Date: Fri Jun 02 00:55:49 2017

VR: Content size incorrect when transitioning from webVR into VR Shell

The issue here is we are setting the virtual display's size when we
enter WebVR, but not when we exit it to VrShell.  This means that
content is incorrectly sized.

The fix simply sets the virtual display's size when we exit WebVR to VrShell.

BUG= 718578 
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2906173002
Cr-Original-Commit-Position: refs/heads/master@{#476074}
Review-Url: https://codereview.chromium.org/2921583003
Cr-Commit-Position: refs/branch-heads/3112@{#108}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}

[modify] https://crrev.com/079395cb4a1ae3e6267aada372111300602ceb2e/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f7b41941ac3c3e7a42d743e5bbae6fe5024edee8

commit f7b41941ac3c3e7a42d743e5bbae6fe5024edee8
Author: billorr <billorr@chromium.org>
Date: Fri Jun 02 04:30:54 2017

Add test for validating the proper size when we exit WebVR to VR browsing.

This is an automated test to validate the fix for crbug/718578.

BUG= 718578 

Review-Url: https://codereview.chromium.org/2918853002
Cr-Commit-Position: refs/heads/master@{#476564}

[modify] https://crrev.com/f7b41941ac3c3e7a42d743e5bbae6fe5024edee8/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java
[modify] https://crrev.com/f7b41941ac3c3e7a42d743e5bbae6fe5024edee8/chrome/android/javatests/src/org/chromium/chrome/browser/vr_shell/VrShellNavigationTest.java

Verified in Chrome Canary 61.0.3123.0