Revert 272472 "Mojo: nuke EnvironmentData"

Revert 272472 "Mojo: nuke EnvironmentData"

Caused layout tests (when run with check-sys-deps) to hang on Windows
with a stuck content_shell process. See Issue 376929.

BUG=376929
> Mojo: nuke EnvironmentData
> 
> With this change, Mojo applications that link against mojo_environment_chromium
> do not need to instantiate mojo::Environment. We rely on AtExitManager for all
> finalization of singleton objects. This frees us up to use the familiar
> base::Singleton and base::LazyInstance for any such state. Tests can use
> ShadowingAtExitManager to clean the environment between test runs.
> 
> It becomes a link error to use mojo::Environment if you are not linking against
> mojo_environment_standalone. I plan to follow this up with a change that buries
> mojo::Environment for the case where you are linking against
> mojo_environment_standalone. Ideally, this means no one will ever need to think
> about mojo::Environment again.
> 
> Review URL: https://codereview.chromium.org/281353005

TBR=darin@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272589

[Ken Russell (switch to Gerrit), 2014-05-23 21:01:51]

Committed patchset #1 manually as r272589.