Roll Dart runtime forward to:

6aab1cecb25f8e04087320f2082336073628afb4

Roll Observatory pub packages to:

5c199c5954146747f75ed127871207718dc87786

---

Update to new isolate create callback signature.

This updates to mojo 4e4d51ce28a and mojo sdk 711a0bcfb141b4 and updates the sky
package's pubspec.yaml dependency to '>=0.1.0 <0.2.0' to be compatible with
the current mojo package. This includes an update to the Mojo Dart generator to
produce real classes for enums and the corresponding updates for users of the
KeyboardType enum in Sky as well as one scoped_ptr->std::unique_ptr in shell
corresponding to a change in the Mojo EDK.

When a new version of the sky and sky_services package are pushed this will fix
domokit/mojo#440.

There's no reason for us to have our own dart-pub-cache in the source tree.  We
can just use the default one on the system.

Updating mojo_sdk to 3ec8c53e9c9e5a8cd3cf251c4ae4754b75172225
Updating mojo_devtools to 49879d78ce4486e10c2214a101d9b2e82794b2f4

This gets rid of the rest of the files in //gpu and the GLES{2,3}
headers from //third_party/khronos. The GL headers used for GLES{2,3}
come from the platform being targetted, that is
//mojo/public/c/gpu/GLES2 for Mojo,
//third_party/android_tools/ndk/platforms/android-XX/usr/include/GLES2
for Android and the OpenGL framework for Mac/iOS.

The //third_party/khronos/EGL headers are still being used by some
utility code in //ui/gl. This code is only really useful on Android, as
Sky doesn't use EGL on iOS/Mac/Mojo, but it's compiled in on all
platforms currently and relies on some EGL defines that are not set in
the EGL headers we currently use. These could probably be removed
without much trouble.

The //third_party/khronos/GLES2 headers are still used by some of
//ui/gl on iOS. These should be using the iOS OpenGL framework headers,
and will in the future.

Removes the unneeded KHRONOS_APICALL override from KHR/khrplatform.h

Rolls to a newer Mojo SDK that doesn't expect //third_party/khronos

Updates the //mojo snapshotted code and the mojo SDK to
0a98559b4, which includes several cleanups in the GL headers.

Also adds /sky/packages/sky_services/lib to .gitignore

This updates to mojo commit d259eb58aa59 and limits the roll script to
only pull in the parts of //mojo that are currently being used. More
stuff will be dropped in the future.

This means that //mojo/public is pulled in by gclient using the hash
specified in the DEPS file from the github.com/domokit/mojo_sdk mirror.
Each mojo_sdk commit corresponds to its originating
github.com/domokit/mojo commit and has the origin commit in the
message. Thus to find the mojo_sdk revision to use for a particular
mojo revision, grep through the commit log in the mojo_sdk repo for the
matching "Cr-Mirrored-Commit:" line.

If you need to back your local checkout to earlier than this commit
after running gclient, do 'rm -rf mojo/public && git reset --hard' to
get the locally checked in versions back.  Otherwise you'll get subtree
commits in mojo/public/... and have a bad time.

This reverts commit 2042a0f0.

Tracking issue https://github.com/domokit/sky_engine/issues/654

This patch makes the sky package match the structure we've adopted for the
other Dart packages we produce from this repo.

We now use `pub` to manage Dart packages.

Fixes #306

TBR=johnmccutchan@google.com

We no longer use sky_server.go. This patch removes it.