Redo: Adding a mojo interface to the mojo spy

This is the same as
https://codereview.chromium.org/284743002

Which was reverted because a mojo refactoring won the checking race
and I did not notice the revert.

Original message:

Adding more guts to the mojo spy.

This CL fleshes out the basic architecture of the spy. Introducing SpyServerImpl and enough code to operate the "start" and "stop" commands of the front-end.

Still a quite a few loose ends, specially on teardown.

I updated the design doc to reflect this CL:
https://docs.google.com/a/chromium.org/document/d/11FKYXf9mSohlsgl4JmGlyWE1ScX3DKdssdjub63tkwA/edit?usp=sharing

TBR=darin
BUG=360188
TEST=manual via test/spy_repl_test.html

Review URL: https://codereview.chromium.org/379753002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281995 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed