Debugging Chromium crashes
If chromium crashes you need to provide a proper backtrace for your crash.
It could be accomplished using gdb and some debug packages.
If you know nothing about gdb, the generic instructions are available here: HowToGetABacktrace
The debug package for chromium is called chromium-browser-dbg (it's big, ~75MB). It could be installed and removed like any other packages.
Note: you may need other debug packages if the backtrace shows lines like "#5 0x083949e0 in ?? ()". In that case, you need the corresponding -dbg or -dbgsym packages.
Once done, open a terminal and proceed as follow:
chromium-browser --debug 2>&1 | tee gdb-chromium.txt (gdb) handle SIG33 pass nostop noprint (gdb) set pagination 0 (gdb) run <arguments, if any>
do what you need to do to trigger the crash, then:
(gdb) backtrace (gdb) thread apply all backtrace (gdb) quit
Check the file gdb-chromium.txt to see if it contains symbols (as few "?? ()" as possible). If not, please locate and install the missing debug package(s) and retry.
Note: ldd /usr/lib/chromium-browser/chromium-browser could give you a clue of which libs are loaded, and http://packages.debian.org/ could tell you in which package they live.
Once you feel it's good enough, you may attach the file gdb-chromium.txt to your bug report.
Note: since chromium is multi-process (it spawns several processes, such as the sandbox and all renderers), the stack may be useless, depending on where the crash occurs. You can then try with --single-process (after --debug). If it is still not enough, you can try inferring from the upstream chrome debugging tips: http://code.google.com/p/chromium/wiki/LinuxDebugging
Debugging GTK Warnings
You can turn a Gtk warning into a crash using the G_DEBUG variable and get a backtrace as above; see the upstream debugging tips for details.