https://bugs.webkit.org/show_bug.cgi?id=101667

Reviewed by Filip Pizlo.

Added a random-eviction based cache for unlinked functions, and switch
UnlinkedFunctionExecutable's code references to Weak<>, thereby letting
us remove the explicit UnlinkedFunctionExecutable::clearCode() calls that
were being triggered by GC.

Refactored the random eviction part of the CodeCache into a separate data
structure so that I didn't have to duplicate the code again, and then used
that for the new function cache.

* bytecode/UnlinkedCodeBlock.cpp:
(JSC::UnlinkedFunctionExecutable::visitChildren):
(JSC::UnlinkedFunctionExecutable::codeBlockFor):
* bytecode/UnlinkedCodeBlock.h:
(JSC::UnlinkedFunctionExecutable::clearCodeForRecompilation):
(UnlinkedFunctionExecutable):
* debugger/Debugger.cpp:
* runtime/CodeCache.cpp:
(JSC::CodeCache::getCodeBlock):
(JSC::CodeCache::generateFunctionCodeBlock):
(JSC::CodeCache::getFunctionExecutableFromGlobalCode):
(JSC::CodeCache::usedFunctionCode):
(JSC):
* runtime/Executable.cpp:
(JSC::FunctionExecutable::clearUnlinkedCodeForRecompilationIfNotCompiling):
(JSC::FunctionExecutable::clearCode):
* runtime/Executable.h:
(FunctionExecutable):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@133975 268f45cc-cd09-0410-ab3c-d52691b4dbfc