Result of the bisect I did locally:
You are probably looking for a change made after 454340 (known good), but no later than 454367 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/08eddf09b057e24f14e20ed473836970d0d8021b..374b2669b0af7cd88882cff28555f5aaa04c52d7

Pointing at my own refactoring CL:
https://codereview.chromium.org/2694543002/

And the bug being due to the fact that after moving |selected_text_| to TextInputManager, I did not remove the variable form RenderWidgetHostViewMac and SpeakSelection still uses that value which is always empty now. Uploading a fix very soon.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b69ac7cd2ccc200ff53b95b30cbbea962a27e0d3

commit b69ac7cd2ccc200ff53b95b30cbbea962a27e0d3
Author: ekaramad <ekaramad@chromium.org>
Date: Mon Apr 24 19:26:31 2017

Fix a recent regression in Speech->Start Speaking on Mac

After a recent refactoring, all RenderWidgetHostViews use TextInputManager in
order to get the value of |selected_text_|. Unfortunately this was not applied
to SpeakText() call inside RenderWidgetHostViewMac and furthermore, the local
variable |selected_text_| was not removed from the view.

BUG=713850

Review-Url: https://codereview.chromium.org/2831183002
Cr-Commit-Position: refs/heads/master@{#466715}

[modify] https://crrev.com/b69ac7cd2ccc200ff53b95b30cbbea962a27e0d3/content/browser/renderer_host/render_widget_host_view_mac.h
[modify] https://crrev.com/b69ac7cd2ccc200ff53b95b30cbbea962a27e0d3/content/browser/renderer_host/render_widget_host_view_mac.mm

Verified on Canary 60.0.3080.5. Going to chrome://version and double tapping "Official" reads the word as expected. Marking as fixed and adding merge request for 59.

Your change meets the bar and is auto-approved for M59. Please go ahead and merge the CL to branch 3071 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), gkihumba@(ChromeOS), Abdul Syed@(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/+/50b0fc38c86e7b9994db4d00c5e5e2247b972a2c

commit 50b0fc38c86e7b9994db4d00c5e5e2247b972a2c
Author: EhsanK <ekaramad@chromium.org>
Date: Thu Apr 27 00:04:03 2017

Fix a recent regression in Speech->Start Speaking on Mac

After a recent refactoring, all RenderWidgetHostViews use TextInputManager in
order to get the value of |selected_text_|. Unfortunately this was not applied
to SpeakText() call inside RenderWidgetHostViewMac and furthermore, the local
variable |selected_text_| was not removed from the view.

BUG=713850

Review-Url: https://codereview.chromium.org/2831183002
Cr-Commit-Position: refs/heads/master@{#466715}
(cherry picked from commit b69ac7cd2ccc200ff53b95b30cbbea962a27e0d3)

Review-Url: https://codereview.chromium.org/2842383002 .
Cr-Commit-Position: refs/branch-heads/3071@{#243}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/50b0fc38c86e7b9994db4d00c5e5e2247b972a2c/content/browser/renderer_host/render_widget_host_view_mac.h
[modify] https://crrev.com/50b0fc38c86e7b9994db4d00c5e5e2247b972a2c/content/browser/renderer_host/render_widget_host_view_mac.mm

Verified this issue on Mac OS 10.12.4 using chrome latest dev M59 #59.0.3071.29 by following steps mentioned in the original comment. 

Observed the words are reading out on enabling start speaking. Hence adding TE-Verified label.

Please refer the screen cast

Deleted: Apr 27 2017 12-56 PM.webm 3.3 MB

	Apr 27 2017 12-56 PM.webm 3.3 MB View Download

 Issue 729406  has been merged into this issue.

If we're going to merge  Issue 729406  into this one then we need to reopen this bug. This regression occurred because we apparently don't have any testing to make sure text-to-speech works. We need to create an automated test for that, or a manual test, but as it stands there's nothing currently stopping this regression from recurring at any time.