The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ed4df89fed450d8f2741bba7cd2651ad28c6a779

commit ed4df89fed450d8f2741bba7cd2651ad28c6a779
Author: ymalik <ymalik@chromium.org>
Date: Mon May 29 19:37:10 2017

Disable back button when stack is empty

If the back stack is empty
- The back button icon's color is that of the foreground with an alpha of 0x33
- Hovering over the back button doesn't change its color

Note:
- tested manually due to time constraints, but we should add a tests

BUG= 726889 

Review-Url: https://codereview.chromium.org/2906403002
Cr-Commit-Position: refs/heads/master@{#475375}

[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/color_scheme.cc
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/color_scheme.h
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/textures/url_bar_texture.cc
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/textures/url_bar_texture.h
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/ui_elements/url_bar.cc
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/ui_elements/url_bar.h
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/ui_scene_manager.cc
[modify] https://crrev.com/ed4df89fed450d8f2741bba7cd2651ad28c6a779/chrome/browser/android/vr_shell/vr_gl_thread.cc

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/+/e8cc130f7fa4718d1656d00276f3303ce48e9393

commit e8cc130f7fa4718d1656d00276f3303ce48e9393
Author: Ian Vollick <vollick@chromium.org>
Date: Tue May 30 12:53:45 2017

Disable back button when stack is empty

If the back stack is empty
- The back button icon's color is that of the foreground with an alpha of 0x33
- Hovering over the back button doesn't change its color

Note:
- tested manually due to time constraints, but we should add a tests

BUG= 726889 

Review-Url: https://codereview.chromium.org/2906403002
Cr-Original-Commit-Position: refs/heads/master@{#475375}
Review-Url: https://codereview.chromium.org/2912953002 .
Cr-Commit-Position: refs/branch-heads/3112@{#26}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}

[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/color_scheme.cc
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/color_scheme.h
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/textures/url_bar_texture.cc
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/textures/url_bar_texture.h
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/ui_elements/url_bar.cc
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/ui_elements/url_bar.h
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/ui_scene_manager.cc
[modify] https://crrev.com/e8cc130f7fa4718d1656d00276f3303ce48e9393/chrome/browser/android/vr_shell/vr_gl_thread.cc

Note that the back button isn't returning to the active state UI when the stack is re-filled. Functionality works, but it keeps it's disabled look. crbug 728435 was logged for this.

Verified in chrome Canary 61.0.3124.3

I'm not sure if this is the same issue resurfacing, but I logged a new bug on the same issue. bug 735143