Roll src/third_party/dart 6fcd1de..270966b (7 commits) (#14553)

https://dart.googlesource.com/sdk.git/+log/6fcd1de98c2c..270966b16044

git log 6fcd1de..270966b --date=short --first-parent --format='%ad %ae %s'
2019-12-18 sjindel@google.com [vm] Fix Fuchsia build of elf_loader.
2019-12-18 brianwilkerson@google.com Remove unnecessary uses of new in analyzer_cli
2019-12-18 brianwilkerson@google.com Remove unnecessary uses of const in analyzer-plugin
2019-12-18 sstrickl@google.com [vm] Reland "Add docs for DWARF stack traces and related tools/libraries."
2019-12-18 sstrickl@google.com [vm] Reland "De-obfuscate function and file names in DWARF sections."
2019-12-18 sstrickl@google.com [vm/compiler] Reland "Add --save-debugging-info flag to gen_snapshot."
2019-12-18 dmitryas@google.com [cfe] Fix bug with assigning an object with .call to a Function

Created with:
  gclient setdep -r src/third_party/dart@270966b16044

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC dart-vm-team@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

Bug: None
Tbr: dart-vm-team@google.com

Author: skia-flutter-autoroll

DEPS

@@ -34,7 +34,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '6fcd1de98c2c946ac6cf0100a8b1c0fad5d4bf3e',
+  'dart_revision': '270966b160442f3ee16f99f9de18b263900c7050',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py

ci/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: d518499e365ef72eca6adbb47d4ae47b
+Signature: 48939ac3d8120cff452043892bb7e0a3
 
 UNUSED LICENSES: