Add @isTest and @isTestGroup to package:meta

R=devoncarew@google.com, paulberry@google.com

Bug: https://github.com/flutter/flutter-intellij/issues/2055
Change-Id: I78083783a3e05171746253101b3b10bbdcc8ef99
Reviewed-on: https://dart-review.googlesource.com/53480
Reviewed-by: Paul Berry <paulberry@google.com>
Reviewed-by: Devon Carew <devoncarew@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/meta/lib/meta.dart

@@ -105,6 +105,22 @@ const _Factory factory = const _Factory();
 ///   class that has this annotation is not immutable.
 const Immutable immutable = const Immutable();
 
+/// Used to annotate a test framework function that runs a single test.
+///
+/// Tools, such as IDEs, can show invocations of such function in a file
+/// structure view to help the user navigating in large test files.
+///
+/// The first parameter of the function must be the description of the test.
+const _IsTest isTest = const _IsTest();
+
+/// Used to annotate a test framework function that runs a group of tests.
+///
+/// Tools, such as IDEs, can show invocations of such function in a file
+/// structure view to help the user navigating in large test files.
+///
+/// The first parameter of the function must be the description of the group.
+const _IsTestGroup isTestGroup = const _IsTestGroup();
+
 /// Used to annotate a const constructor `c`. Indicates that any invocation of
 /// the constructor must use the keyword `const` unless one or more of the
 /// arguments to the constructor is not a compile-time constant.
@@ -244,6 +260,14 @@ class _Factory {
   const _Factory();
 }
 
+class _IsTest {
+  const _IsTest();
+}
+
+class _IsTestGroup {
+  const _IsTestGroup();
+}
+
 class _Literal {
   const _Literal();
 }