Fix a small race condition in loading/executing the PPAPI tests.
Fix a small race condition in loading/executing the PPAPI tests.

BUG=none
TEST=PPAPI tests still pass (perhaps even less flakily)


Review URL: http://codereview.chromium.org/8468017

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@110203 0039d316-1c4b-4281-b951-d872f2087c98

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