This is because compiler.cc is awesome. There are cases where we do not
yet have a SharedFunctionInfo that can tell us whether we are compiling
a generator function, we query the FunctionLiteral instead.

R=rmcilroy@chromium.org
BUG=v8:4681
LOG=n

Review URL: https://codereview.chromium.org/1780193002

Cr-Commit-Position: refs/heads/master@{#34677}