[kernel] Make snapshotting work.

[kernel] Make snapshotting work.

This CL enables snapshotting for kernel.
Basically what it does is that it writes out and reads in a few
previously missing entries in the snapshot file (from  Field, Function
and Script).

Debugging from a snapshot made from kernel will not work as snapshots
does not contain sourcecode (it is normally synthesized from the
TokenStream which doesn't exist in kernel).

BUG=
R=kmillikin@google.com

Committed: https://github.com/dart-lang/sdk/commit/60ed069e7cdbebc266773fd4643cd9227f3f28ee

[jensj, 2017-08-03 13:03:48]

Notice that this builds on top of other currently un-landed CLs.

Only tested on helloworld.dart file
```
main() {
  print("Hello, World!");
}
```
(okay, it also fixed a few tests so I guess implicitly it was tested on other
stuff too)
as follows:

```
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ type runWithKernel
runWithKernel is aliased to
`/usr/local/google/home/jensj/code/dart-sdk/sdk/out/ReleaseX64/dart  
--dfe=/usr/local/google/home/jensj/code/dart-sdk/sdk/utils/kernel-service/kernel-service.dart
 
--kernel-binaries=/usr/local/google/home/jensj/code/dart-sdk/sdk/out/ReleaseX64/patched_sdk
  --packages=/usr/local/google/home/jensj/code/dart-sdk/sdk/.packages'


jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ time runWithKernel helloworld.dart
Hello, World!

real    0m1.501s
user    0m2.000s
sys     0m0.220s


jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ runWithKernel
--snapshot=hello.dart.snapshot --snapshot-kind=app-jit helloworld.dart
Hello, World!
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ out/ReleaseX64/dart
hello.dart.snapshot
Hello, World!
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ time out/ReleaseX64/dart
hello.dart.snapshot
Hello, World!

real    0m0.122s
user    0m0.132s
sys     0m0.024s
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ ls -lha hello.dart.snapshot
-rw-r----- 1 jensj eng 3.5M Aug  3 10:42 hello.dart.snapshot



jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ runWithKernel
--snapshot=hello.dart.snapshot helloworld.dart
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ out/ReleaseX64/dart
hello.dart.snapshot
Hello, World!
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ time out/ReleaseX64/dart
hello.dart.snapshot
Hello, World!

real    0m0.170s
user    0m0.180s
sys     0m0.024s
jensj@jensj-goobuntu1:~/code/dart-sdk/sdk$ ls -lha hello.dart.snapshot
-rw-r----- 1 jensj eng 191K Aug  3 11:24 hello.dart.snapshot
```

[jensj, 2017-08-03 13:04:58]

jensj@google.com changed reviewers:
+ kmillikin@google.com, sivachandra@google.com

[Kevin Millikin (Google), 2017-08-09 09:37:40]

LGTM.

[jensj, 2017-08-10 08:26:32]

Description was changed from

==========
[kernel] Make snapshotting work.

This CL enables snapshotting for kernel.
Basically what it does is that it writes out and reads in a few
previously missing entries in the snapshot file (from  Field, Function
and Script).

Debugging from a snapshot made from kernel will not work as snapshots
does not contain sourcecode (it is normally synthesized from the
TokenStream which doesn't exist in kernel).

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

to

==========
[kernel] Make snapshotting work.

This CL enables snapshotting for kernel.
Basically what it does is that it writes out and reads in a few
previously missing entries in the snapshot file (from  Field, Function
and Script).

Debugging from a snapshot made from kernel will not work as snapshots
does not contain sourcecode (it is normally synthesized from the
TokenStream which doesn't exist in kernel).

BUG=
R=kmillikin@google.com

Committed:
https://github.com/dart-lang/sdk/commit/60ed069e7cdbebc266773fd4643cd9227f3f28ee
==========

[jensj, 2017-08-10 08:26:36]

Committed patchset #1 (id:1) manually as
60ed069e7cdbebc266773fd4643cd9227f3f28ee (presubmit successful).