Bundle the DEPS of mojom_bindings_generator.py with the public SDK.

The rationale for this bundling is the following:
- Every client of the public SDK will need these deps to process the mojoms in
the public SDK.
- These deps are not something that clients will already have in general (as
opposed to say a C++ compiler).
- Even if the client happens to already have these deps, by packaging the
versions that mojom_bindings_generator.py is interfaced against we make
mojom_bindings_generator.py hermetic.

Note that the versions of these modules in //third_party are left there because
there are other internal dependencies on them throughout the repo.

R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/801523002