[release] Prepare the CHANGELOG for 2.7.0

TBR=whesse@google.com

Change-Id: I3ba75be4eb7194ded270179c842ed8949a75d4ec
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127480
Reviewed-by: Alexander Thomas <athom@google.com>

Author: athomas

CHANGELOG.md

@@ -4,6 +4,28 @@
 
 ### Language
 
+### Core libraries
+
+#### `dart:io`
+
+### Dart VM
+
+### Tools
+
+#### Linter
+
+The Linter was updated to `0.1.105+1`, which includes:
+
+* hardened checks for lib dir location (fixing crashes in `avoid_renaming_method_parameters`,
+  `prefer_relative_imports` and `public_member_api_docs`)
+* improved performance for `always_require_non_null_named_parameters`
+
+#### Pub
+
+## 2.7.0 - 2019-12-11
+
+### Language
+
 * **Breaking Change**: [Static extension members][] are accessible when
 imported with a prefix (issue [671][]). In the extension method **preview**
 launch, importing a library with a prefix hid all extension members in
@@ -48,11 +70,11 @@ program-defined, whereas previously it was undefined.
 
 #### Linter
 
-The Linter was updated to `0.1.105+1`, which includes:
+The Linter was updated to `0.1.104`, which includes:
 
-* hardened checks for lib dir location (fixing crashes in `avoid_renaming_method_parameters`,
-  `prefer_relative_imports` and `public_member_api_docs`)
-* improved performance for `always_require_non_null_named_parameters`
+* updated `unnecessary_overrides` to allow overrides when annotations (besides `@override` are specified)
+* updated `file_names` to allow names w/ leading `_`'s (and improved performance)
+* new lint: `unnecessary_final`
 
 #### Pub