Package map processing tests.

Package map processing tests.

Follow-up from https://codereview.chromium.org/2043963004/, where a number of test cases were identified.  In particular:

> - What if the package map is empty?
> - What if the package map doesn't have a package with an embedder file?
> - What is there is no package with an ext?
> - What if we don't find either one?
> - What happens if one or both of those files are invalid?

BUG=
R=brianwilkerson@google.com

Committed: https://github.com/dart-lang/sdk/commit/df4ea535938fe2e967ebcb14ef4537ea92f836bd

[pquitslund, 2016-06-07 21:19:32]

pquitslund@google.com changed reviewers:
+ brianwilkerson@google.com

[Brian Wilkerson, 2016-06-07 22:00:06]

lgtm

[pquitslund, 2016-06-07 22:04:34]

Description was changed from

==========
Package map processing tests.

Follow-up from https://codereview.chromium.org/2043963004/, where a number of
test cases were identified.  In particular:

> - What if the package map is empty?
> - What if the package map doesn't have a package with an embedder file?
> - What is there is no package with an ext?
> - What if we don't find either one?
> - What happens if one or both of those files are invalid?

BUG=
==========

to

==========
Package map processing tests.

Follow-up from https://codereview.chromium.org/2043963004/, where a number of
test cases were identified.  In particular:

> - What if the package map is empty?
> - What if the package map doesn't have a package with an embedder file?
> - What is there is no package with an ext?
> - What if we don't find either one?
> - What happens if one or both of those files are invalid?

BUG=
R=brianwilkerson@google.com

Committed:
https://github.com/dart-lang/sdk/commit/df4ea535938fe2e967ebcb14ef4537ea92f836bd
==========

[pquitslund, 2016-06-07 22:04:35]

Committed patchset #1 (id:1) manually as
df4ea535938fe2e967ebcb14ef4537ea92f836bd (presubmit successful).