<chromium> Add ifdefs to exclude ATL and accessibility from the build

ATL currently isn't distributed with MSVS Express, only with the
Professional version. Chromium requires downloading the WDK iso for
express users just to be able to use the ATL version that was shipped
with it.

We can avoid the extra dependency for now by cutting off all the
accessibility code, which is currently the only part of the content
layer depending on ATL. We will use the Qt accessibility code anyway.

Change-Id: Iec25231250ccfc9405fdf342752733814888f348
Reviewed-by: Andras Becsi <andras.becsi@digia.com>