* Add metadata to requests to pub.dartlang.org.

This will help pub.dartlang.org better track how packages relate to one
another.

* Fix broken depenency tests.

Those unit tests import pub libraries directly without invoking a
command, so command was throwing an exception. Worse, the Pokemon
exception handler in DependencyValidator was then catching the
StateError, hiding the bug.

Also applied some other changes I suggested.

Get the Mac tests passing again with the mtree stuff in tar.

run dartfmt

Closes #1519

"git ls-files" doesn't recurse into submodules, so we need to do so
manually.

Closes #1523

Fixes #1442

I'm not sure why this wasn't causing us problems before.

Closes #1514

This adds a validator that warns when a package incorrectly imports a non-dependency.

R=nweiz@google.com, rnystrom@google.com

BUG= https://github.com/dart-lang/pub/issues/1511

Review-Url: https://codereview.chromium.org//2653753010 .

Fix two strong-mode warnings

Disable passing "--uname" and "--gname" to tar on non-Linux.

That hits OS X too, and the version of tar on OS X doesn't support
those. :(

Run executables in Isolates.

We had previously been running executables in sub-processes, which made
it difficult to ensure that those executables handled signals and
standard IO properly, and impossible to give them an accurate view of
the environment (for example via Stdout.hasTerminal).

Closes #1204

It seems like dart-lang/sdk#12617 got fixed at some point.

When writing to a symlinked file using dart:io, it defaults to
overwriting the contents of the target rather than replacing the
symlink. This is never what we want, so this works around the behavior
in our IO wrappers.

Closes #1493

Pub no longer outputs the "Loading source assets..." line in this case.

The test is failing on the buildbots, and locally.

This also changes tar creation on Linux to use "pub" as the user/group
rather than the ID 0, so people don't accidentally end up manually
extracting files with root ownership.

Closes #1442

3fa5df4d added new flags between the
"--directory" flag and the directory in question, which broke untarring.

In particular, "pub get --offline" and "pub cache repair" shouldn't
choke when there are parse failures in the version cache.

Closes #1479

Closes #1482.

Avoid barback for global operations.

Add two flags to `tar` invocation that will provide consistent behavior whether `pub` is executed as root or a normal user.

Closes #1486 

Closes #1477

Similarly 98ecbded, this provides better
error messages and faster installation times.

See #1473
See #1477

Previously we were always loading an AssetEnvironment when we
precompiled any executable. Now we only load that environment if some
package dependended on by some executable actually uses a transformer.
Otherwise, we precompile from disk. The new approach is substantially
faster and produces better error messages.

Closes #1473