Adds a cache (PersistenUnitCache) to store CompilationUnits
between invocations of DevMode and the Compiler.  This
saves time in building the TypeOracle on startup for those
files that have 1) remained unchanged and 2) their type
dependencies have remained unchanged as well.

The cache is off by default.  Enable it with the
-Dgwt.persistentunitcache system property

Review at http://gwt-code-reviews.appspot.com/1375802


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9893 8db76d5a-ed1c-0410-87a9-c151d255dfc7
26 files changed