By adding LoadIC support for JSModuleNamespace objects. The index
of the corresponding slot in the Module's "exports" dictionary is
cached in the feedback vector, so the value can be loaded directly,
without having to call the C++ accessor.
This speeds up the "foo" property access in code like the following
snippet by about 10x:
  import * as m from "module.js"
  m.foo;

Bug: v8:1569
Change-Id: I152abedcbdc6f90b5bedd203cfdf97ed88d1137c
Reviewed-on: https://chromium-review.googlesource.com/631136
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47625}