See Running GLib Applications for notes on how to make GTK warnings fatal.
sudo apt-get install libgtk-3-0-dbg
Make sure that you're building a binary that matches your architecture (e.g. 64-bit on a 64-bit machine), and there you go.
You‘ll likely want to get the source for gtk too so that you can step through it. You can tell gdb that you’ve downloaded the source to your system's GTK by doing:
$ cd /my/dir $ apt-get source libgtk-3-0 $ gdb ... (gdb) set substitute-path /build/buildd /my/dir
NOTE: I tried debugging pango in a similar manner, but for some reason gdb didn't pick up the symbols from the symbols from the -dbg package. I ended up building from source and setting my LD_LIBRARY_PATH.
See building_debug_gtk.md for more on how to build your own debug version of GTK.
http://chipx86.github.com/gtkparasite/ is great. Go check out the site for more about it.
Install it with
sudo apt-get install gtkparasite
And then run Chrome with
GTK_MODULES=gtkparasite ./out/Debug/chrome
Use GDK_DEBUG=nograbs to run GTK+ without grabs. This is useful for gdb sessions.