Add support for a target new space size

Add support for a target new space size

When this flag is set, we will commit additional pages up until the
target size before doing a scavenge.

I made sure that all tests pass when a target size of 16MB is set.

BUG=v8:3626
R=ulan@chromium.org
LOG=n

Committed: https://code.google.com/p/v8/source/detail?r=24790

[ulan, 2014-10-21 15:01:50]

lgtm

https://codereview.chromium.org/652543007/diff/1/src/heap/spaces.cc
File src/heap/spaces.cc (right):

https://codereview.chromium.org/652543007/diff/1/src/heap/spaces.cc#newcode1312
src/heap/spaces.cc:1312: V8::FatalProcessOutOfMemory("Failed to grow new
space.");
All V8::FatalProcessOutOfMemory here should be CHECK since they cannot not
happen.

[jochen (gone - plz use gerrit), 2014-10-22 06:58:50]

Committed patchset #2 (id:20001) manually as 24790 (presubmit successful).