It was previously the case that instrumentStart in ASanInstrumentation would block until instrumentGlobals had completed. This was because instrumentStart depends on the global redzones having been inserted. However, instrumentGlobals was not called until the first function was popped off the emit queue, and when _start was the first function, it was not placed on the emit queue until after it had been instrumented and lowered. instrumentStart was waiting for instrumentGlobals, which could not happen until instrumentStart completed.

BUG=https://bugs.chromium.org/p/nativeclient/issues/detail?id=4374
R=kschimpf@google.com, stichnot@chromium.org

Review URL: https://codereview.chromium.org/2165493002 .