Google Chrome 66.0.3329.1 (Official Build) canary (64-bit) (cohort: Clang-64)
Windows 10 Enterprise Version 1607 Build 14393.2007
NVDA 2017.4
JAWS 2018.1801.18 Private Beta 

This was reported to me by a developer @nektar so I'll note where his experience differs from mine. 

Steps to repro:
# Launch JAWS
# Navigate to chrome://settings/passwords or Chrome > Settings > Manage Passwords 
# Navigate to any saved password and invoke the "view password" button, note that JAWS says Show password Button without issue. 
# Windows OS prompt appears. It appears as a modal when using Chrome, blocking accessing other parts of Chrome browser. However, I am able to shift + tab to other parts of the OS such as other programs and use them without issue. Unlike a permissions prompt, this prompt doesn't block everything in the OS. 

For me, the prompt was read automatically when it appeared, but it did not say the text at the top such as "Windows Security". After that, I was unable to access the content in the prompt except for tabbing to the "more options", OK, and Cancel buttons. Arrow keys only navigated between the OK and Cancel buttons. 

For @nektar, the prompt is not read at all. He was unable to tell that this a Windows prompt, not a Chrome prompt. 

# Enter your Windows credentials, accept the dialog by pressing enter. 
# Focus returns to the Chrome passwords page, now with the password visible. 

With the latest version of JAWS, the content in Chrome is read. The last time I tried this with a slightly older version of JAWS, nothing was read. Note that JAWS reads it as static text, not as an edit box that uses forms mode. JAWS said "read only edit" and forms mode is off. I can navigate across it with the arrow keys to read it character by character.   

# Repeat all the above steps with NVDA 
On the Windows dialog, all content is spoken including the "Windows Security" text at the top.

Once the Windows dialog is read, I'm not able to navigate to get that content to read again with arrow keys or tabbing. 

When I am navigating across the newly uncovered password, NVDA sees it as a text entry field and goes into forms mode. To read the password character by character, I need to go into focus mode and then navigate across it with the arrow keys.