Move interpreter cctests into v8::internal::interpreter namespace.

Move interpreter cctests into v8::internal::interpreter namespace.

This moves the cctest file for the interpreter to live in the same
namespace as the components it is testing. Hence we can avoid the
forbidden using directives pulling in entire namespaces.

From the Google C++ style guide: "You may not use a using-directive to
make all names from a namespace available". This would be covered by
presubmit linter checks if build/namespaces were not blacklisted.

R=rmcilroy@chromium.org

Committed: https://crrev.com/d1805edada73aafb751ebc1a3d6d12262b53acb7
Cr-Commit-Position: refs/heads/master@{#31681}

[rmcilroy, 2015-10-30 10:41:02]

LGTM, thanks! (I did this originally because it seemed like cctest wouldn't run
the tests as tests if they weren't in the outer namespace, but I guess I had
messed something else up :/)

[Michael Starzinger, 2015-10-30 10:47:25]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-10-30 10:47:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1410993009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1410993009/1

[commit-bot: I haz the power, 2015-10-30 11:05:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-30 11:05:58]

Patchset 1 (id:??) landed as
https://crrev.com/d1805edada73aafb751ebc1a3d6d12262b53acb7
Cr-Commit-Position: refs/heads/master@{#31681}