Squeeze the layout of various AST node types.

The following AST node types were improved (in decreasing number of
importance for asm.js-like source code): Expression, VariableProxy,
Assignment, BinaryOperation, Declaration, Property, Call.

BUG=chromium:417697
LOG=y
R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/646803004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24593 ce2b1a6d-e550-0410-aec6-3dcde31c8c00