Bring config.h.in up to date.

Bring config.h.in up to date.

Chromium today has its own config.h
(over here
http://src.chromium.org/svn/trunk/src/webkit/config.h.in), which was forked
a while back from webkit's config.h. I'm preparing the ground for the webkit
port, I'm depreciating chromium's config.h and moving its chromium-specific
defines into the ifdef PLATFORM(CHROMIUM) section of webkit's config.h.

Due the complexity of this step, it is broken into three steps:
Step 1: Merge in changes from webkit's config.h into chromium's config.h.in.
Step 2: Copy config.h.in into webkit as the new config.h.
Step 3: Delete chromiums config.h.in and make it use webkit's config.h.

THIS PATCH IS FOR STEP 1.

Patch by yaar@chromium.org, see review here:
http://codereview.chromium.org/201056

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=25776