NaCl: Move src/trusted/plugin/ to components/nacl/renderer/plugin/

This moves the "trusted plugin" code so that all the NaCl
renderer-side code is in the same place, under
components/nacl/renderer/.  I've used the "renderer/plugin/" subdir so
that this legacy code is distinguished from the newer code that's
directly under "renderer/".

This will make further incremental cleanups easier: It will enable
closer integration between renderer/* and renderer/plugin/*.  Rather
than indirecting through PPB_NaCl_Private/PPP_PexeStreamHandler, it
would be reasonable for the two sides to share pointers to C++
objects.  Doing that will be more acceptable when the two sides live
in the same directory.

 * chrome/chrome_tests.gypi: Declaring a runtime dependency isn't
   necessary since the trusted plugin isn't a separate DSO/DLL these
   days.

 * .gitignore: Remove reference to ppGoogleNaClPluginChrome.xml, which
   no longer exists.

 * module_ppapi.h: Added an #include guard.

BUG=239656
TEST=trybots

Review URL: https://codereview.chromium.org/876483002

Cr-Commit-Position: refs/heads/master@{#313759}
44 files changed