Roll dart to 7764e69. (flutter#4960)

* Roll dart to 7764e69.

Changes since last roll:

```
7764e69 Initial API to build analysis contexts (replaces ContextLocator.locateContexts)
5ea271b Clean up documentation of implicit new/const insertions tests.
cf93009 Removed the magic const feature from implicit-creation.md
bd39320 Recover from error on undefined continue label.
5d89a1a Add tests for mixin application constructor forwarding.
e696279 Use import URIs when invalidating files
23c59bd Fix compare_failures
290cc58 Use actual receiver when error-wrapping a null-aware property get.
34763bc Reland "[VM] Introduction of type testing stubs - Part 1-4"
a86b864 Handle updated .packages in incremental compiler
f555ae5 Trust type annotations in strong mode
0a4a3be When cloning YieldStatement, copy the flags
91bbc79 Skip abstract forwarding stubs
7689dc9 Bring in the latest pub_semver
f71d204 Fix expected type in substByContext
5e99872 Improve missing/invalid type reference recovery
899dbe4 Forward type arguments in one-shot interceptors.
1fd3011 dart2js: Add more whole-program information to dump-info
5e23c28 Revert "[infra] Temporarily disable Windows SDK builder on CQ"
2471888 Serialize any MethodInvocation as possible const.
b430570 dart2js: handle constant casts with type variable substitutions
3575b81 Only add const in a constant context (issue 32819)
09f7d2a dart2js: naive support for instantiations in constants - ignore the actual instantiation
4dd5e6e js_runtime: fix _JsonMap keys list type
71ffe97 Correctly handle constant fields when computing constness (take 2)
d58b0e2 [VM] Mark bigint test slow after small Smi change
1e997ee Revert "Reland "[VM] Introduction of type testing stubs - Part 1-4""
00097ad Remove reference to deprecated setter
cb065a1 [infra] Update checked-in SDK version to 2.0.0-dev.46.0
0e9a77a [VM] Reduce Smi size to 32 bit on 64 bit platforms
34bfefd [gardening] Update status file
969c0de Avoid crash on EOF error in file with Windows line encoding
8054409 Reland "[VM] Introduction of type testing stubs - Part 1-4"
```

* Ignore freetype2 in skia since 'we use our own version'

* Update license hash

DEPS

@@ -31,7 +31,7 @@ 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': 'ef926f98f525b085e1488be8c42b1c3f0a24c50d',
+  'dart_revision': '7764e6962e22afcf4b58c4e3cef3147330f3c884',
 
   'dart_args_tag': '1.4.1',
   'dart_async_tag': '2.0.6',
@@ -46,7 +46,7 @@ vars = {
   'dart_convert_tag': '2.0.1',
   'dart_crypto_tag': '2.0.2+1',
   'dart_csslib_tag': '0.14.1',
-  'dart_dart2js_info_tag': '0.5.5+1',
+  'dart_dart2js_info_tag': '0.5.6',
   'dart_dart_style_tag': '1.0.10',
   'dart_dartdoc_tag': 'v0.18.1',
   'dart_fixnum_tag': '0.10.5',
@@ -60,7 +60,7 @@ vars = {
   'dart_intl_tag': '0.15.2',
   'dart_isolate_tag': '1.1.0',
   'dart_json_rpc_2_tag': '2.0.6',
-  'dart_linter_tag': '0.1.46',
+  'dart_linter_tag': '0.1.47',
   'dart_logging_tag': '0.11.3+1',
   'dart_markdown_tag': '1.1.1',
   'dart_matcher_tag': '0.12.1+4',
@@ -76,7 +76,7 @@ vars = {
   'dart_pool_tag': '1.3.4',
   'dart_protobuf_tag': '0.7.1',
   'dart_pub_rev': '4947e0b3cb3ec77e4e8fe0d3141ce4dc60f43256',
-  'dart_pub_semver_tag': '1.3.4',
+  'dart_pub_semver_tag': '1.3.6',
   'dart_quiver_tag': '5aaa3f58c48608af5b027444d561270b53f15dbf',
   'dart_resource_rev': 'af5a5bf65511943398146cf146e466e5f0b95cb9',
   'dart_root_certificates_rev': '16ef64be64c7dfdff2b9f4b910726e635ccc519e',

tools/licenses/lib/main.dart

@@ -1809,6 +1809,7 @@ class RepositorySkiaThirdPartyDirectory extends RepositoryGenericThirdPartyDirec
   bool shouldRecurse(fs.IoNode entry) {
     return entry.name != 'giflib' // contains nothing that ends up in the binary executable
         && entry.name != 'freetype' // we use our own version
+        && entry.name != 'freetype2' // we use our own version
         && entry.name != 'icu' // we use our own version
         && entry.name != 'libjpeg-turbo' // we use our own version
         && entry.name != 'libpng' // we use our own version

travis/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: 5e7a29bc2be55a7311df8f5a7dff2d34
+Signature: bea26d7863b6f1cfa1d0c0ae3775bf93
 
 UNUSED LICENSES: