Adds a meta-target "//base/allocator" that forwards to tcmallor or nothing depending on the build configuration.
Write tcmalloc target definition.
Write base unit tests prefs, and some support targets from base.gypi.
Fix a bunch of added files in the base target that were exposed by linking the unit tests.
Removes toolkit_uses_gtk which was removed from the GYP build.
BUG=
R=scottmg@chromium.org
Review URL: https://codereview.chromium.org/288203003
git-svn-id: http://src.chromium.org/svn/trunk/src/build@271079 4ff67af0-8c30-449e-8e8b-ad334ec8d88c