* Roll dart.

Changes since last roll:

4da52281aa [frontend-server] Return non-zero exit code if there are errors.
d7a540bfe7 Document --enable-asserts in dart2js's help, and remove --checked.
d9c3190e44 [vm] Remove some bin -> vm includes.
3dcdaf9e57 [vm] Check for OOM when allocating a new handle block.
865f52737a [dart:io] Adds IOOverrides.socketConnect
f858e5d539 Replace Token.previous usage in BodyBuilder
f66532b31b Replace more occurrences of token.previous with findPrevious
d46915d239 Bring in the latest pub
7470f410dd Clean up documentation of command-line analyzer options
4b682341d9 [ VM / Dart 2 ] Marked tests that exercise functionality not supported in Dart 2 as SkipByDesign.
859632b439 Fixes for uninitialized fields of Flutter widgets create constructors in Flutter style.
c9e9c1d8e9 Remove dart:isolate runtime support in DDC
0482cf4da1 [fuchsia] Add rules to build gen_snapshot targeting Fuchsia
2de82410e0 Make isolate patch play nice with web workers.
be3baa0b8f Additional ExprBuilder implementation.
42581e4fa6 [VM] Added '--enable-asserts' to the top-level help message.
44dbba2b80 Use offset/length of the import prefix, or empty. Same for constructor names.
85b4c604c5 [VM runtime] Improve type error messages in Dart 2 (fixes #32564). Hide private class _Future and map it to core lib class Future. In Dart 2, show dynamic as type argument(s) of raw generic types.
ebdee7ee0f More prep work to allow the linker to re-use resolution logic.
91e6c8b019 Fix missing_return warning in expr_builder.dart
59de9710ea Complete Flutter's setState() as a whole statement, with a closure, and the caret inside the closure.
b82e5b4704 Replace code completion usage of token.previous with findPrevious
0e8457c8c8 Fix for building sequence of identifiers and several tests.
6a84638d7a Updated for proper failure.
577b168c39 Fix jsinterop bug: we incorrectly added null values for js-interop constructor calls.
8e02ff92db Added @category annotation for Web libraries and removed createCustomUpgrader.
c60199cf86 [vm/kernel/aot] Tree shaking based on results of TFA, take 2.
b217e21907 Mark a few more co19 failures to fix.
70f455351d [kernel] Add field for instantiate-to-bounds algorithm in TypeParameter.
bc75856e54 Update getClientRects, removed xtab, removed bogus entry in dom.json, expose ServiceWorker, removed query and queryAll from in dart:html, added constructor to MessageChannel and removed getCssCanvasContext.
f9e12f1116 step 3 of ??: ignore old options from old FE
c0fa4e2fe3 step 2 of ??: remove unnecessary pattern in -m option
51867f28a2 step 1 of ??: cleaning up options...

* Update license hash. No license changes.