The reason why you're seeing this low contrast is because of a change to Google Chrome's user interface (UI) that took place in version 69. Certain aspects of the UI no longer obey the user's gtk theme. A bug has been filed in this regard and one can star GTK+ theme ignored in omnibar in the new interface.
You can solve the contrast issue described in your question by applying the workaround described in the Ask Ubuntu link above.
The image below uses the "default" mode which is the new mode present in version 69. Note the somewhat rounded tab corners and the low contrast for entries in the dropdown:
The next image uses the "normal" mode which retains the tab design of version 68 (and earlier) and also provides better visual contrast for the selected item in the dropdown just as you would expect from your current gtk theme:
Both images were taken with the Adwaita theme and Google Chrome Version 69.0.3497.92 (Official Build) (64-bit).
The reason why you're seeing this low contrast is because of a change to Google Chrome's user interface (UI) that took place in version 69. Certain aspects of the UI no longer obey the user's gtk theme. A bug has been filed in this regard and one can star GTK+ theme ignored in omnibar in the new interface.
There is a workaround, for now, described in How to get back my previous omnibox in Google Chrome 69 or Chromium 69?.
You can solve the contrast issue described in your question by applying the workaround described in the Ask Ubuntu link above.
The image below uses the "default" mode which is the new mode present in version 69. Note the somewhat rounded tab corners and the low contrast for entries in the dropdown:
The next image uses the "normal" mode which retains the tab design of version 68 (and earlier) and also provides better visual contrast for the selected item in the dropdown just as you would expect from your current gtk theme:
Both images were taken with the Adwaita theme and Google Chrome Version 69.0.3497.92 (Official Build) (64-bit).