[Win] Avoid unnecessary asserts if "prepareToPlay" is called multiple times.
https://bugs.webkit.org/show_bug.cgi?id=128859

Reviewed by Eric Carlson.

* platform/graphics/avfoundation/cf/MediaPlayerPrivateAVFoundationCF.cpp:
(WebCore::AVFWrapper::createPlayer): Don't assert if player exists; just return the
existing copy.
(WebCore::AVFWrapper::createPlayerItem): Ditto (but with Player Items).


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@164177 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Unreviewed, roll out r164166.

This broke three unique tests:

** The following JSC stress test failures have been introduced:
    regress/script-tests/variadic-closure-call.js.default-ftl
    regress/script-tests/variadic-closure-call.js.ftl-no-cjit-validate
    regress/script-tests/variadic-closure-call.js.ftl-no-cjit-osr-validation
    regress/script-tests/variadic-closure-call.js.ftl-eager
    regress/script-tests/variadic-closure-call.js.ftl-eager-no-cjit
    regress/script-tests/variadic-closure-call.js.ftl-eager-no-cjit-osr-validation
    jsc-layout-tests.yaml/js/script-tests/unmatching-argument-count.js.layout-ftl-eager-no-cjit
    regress/script-tests/direct-arguments-getbyval.js.ftl-eager-no-cjit
    regress/script-tests/direct-arguments-getbyval.js.ftl-eager-no-cjit-osr-validation

* bytecode/PolymorphicAccessStructureList.h:
* ftl/FTLCapabilities.cpp:
(JSC::FTL::canCompile):
* ftl/FTLLowerDFGToLLVM.cpp:
(JSC::FTL::LowerDFGToLLVM::compileNode):
* tests/stress/ftl-getbyval-arguments.js:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@164178 268f45cc-cd09-0410-ab3c-d52691b4dbfc