Reduce initial boot-up memory use. This is an other attempt at what

Reduce initial boot-up memory use.  This is an other attempt at what
http://codereview.chromium.org/9179012 was trying to achieve.  This
time I am going for 80% of the benefit with around 5% of the complexity.

It works by reducing the size of the first page in each space.  Unlike the
previous change there is no attempt to grow pages, we just allocate more
full-sized pages when we need more memory.  For this reason the first pages are
not quite as small (compare
http://codereview.chromium.org/9179012/diff/1/src/snapshot.h with the changes
in spaces.cc in this cl):  We want to be able to do a little bit of allocation
before we have to add a full-sized page to the space.
Review URL: https://chromiumcodereview.appspot.com/9950048

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11203 ce2b1a6d-e550-0410-aec6-3dcde31c8c00