Prepare for release 2.60.0 (#9880)

* Prepare for release 2.60.0

* flutter-candidate-ad80825c24d770a19e33f67800fc0338a3b89ec7

flutter-candidate.txt

diff --git a/flutter-candidate.txt b/flutter-candidate.txt
index 7a15421..5900694 100644
--- a/flutter-candidate.txt
+++ b/flutter-candidate.txt
@@ -1 +1 @@
-7e1e507403236215dd7420e1b2bb5dc5895554ce
+ad80825c24d770a19e33f67800fc0338a3b89ec7

packages/devtools_app/lib/devtools.dart

diff --git a/packages/devtools_app/lib/devtools.dart b/packages/devtools_app/lib/devtools.dart
index 5d9d594..32991b3 100644
--- a/packages/devtools_app/lib/devtools.dart
+++ b/packages/devtools_app/lib/devtools.dart
@@ -10,4 +10,4 @@
 /// Note: a regexp in the `dt update-version' command logic matches the constant
 /// declaration `const version =`. If you change the declaration you must also
 /// modify the regex in the `dt update-version' command logic.
-const version = '2.60.0-dev.0';
+const version = '2.60.0';

packages/devtools_app/pubspec.yaml

diff --git a/packages/devtools_app/pubspec.yaml b/packages/devtools_app/pubspec.yaml
index f4fe7bf..51a8731 100644
--- a/packages/devtools_app/pubspec.yaml
+++ b/packages/devtools_app/pubspec.yaml
@@ -7,7 +7,7 @@
 
 # Note: this version should only be updated by running the 'dt update-version'
 # command that updates the version here and in 'devtools.dart'.
-version: 2.60.0-dev.0
+version: 2.60.0
 
 repository: https://github.com/flutter/devtools/tree/master/packages/devtools_app