[linter] Dot shorthands: Add tests for omit_obvious_types.

Make sure that we're not suggesting to omit types for these two lints with dot shorthands, which shouldn't be the case since we didn't add extra logic for `hasObviousType`.

Added a few tests.

Fixes: https://github.com/dart-lang/sdk/issues/60910
Bug: https://github.com/dart-lang/sdk/issues/60893
Change-Id: If088ad7e5ed1d2ed7f202a462baab5461ae046fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/434541
Commit-Queue: Kallen Tu <kallentu@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>

pkg/linter/test/rules/omit_obvious_local_variable_types_test.dart

@@ -58,6 +58,18 @@ class A {
     );
   }
 
+  test_cascade_dotShorthand() async {
+    await assertNoDiagnostics(r'''
+f() {
+  A a = .new()..x..x..x;
+}
+
+class A {
+  final x = 0;
+}
+''');
+  }
+
   test_dot_shorthand() async {
     await assertNoDiagnostics(r'''
 f() {
@@ -77,6 +89,16 @@ f() {
     );
   }
 
+  test_forEach_inferredList_dotShorthands() async {
+    await assertNoDiagnostics(r'''
+enum E { a, b, c }
+
+f() {
+  for (E e in [.a, .b, .c]) { }
+}
+''');
+  }
+
   test_forEach_listWithNonObviousElement() async {
     await assertNoDiagnostics(r'''
 f() {
@@ -183,6 +205,16 @@ class A {}
     );
   }
 
+  test_instanceCreation_nonGeneric_dotShorthand() async {
+    await assertNoDiagnostics(r'''
+f() {
+  A a = .new();
+}
+
+class A {}
+''');
+  }
+
   test_list() async {
     await assertDiagnostics(
       r'''
@@ -194,6 +226,16 @@ f() {
     );
   }
 
+  test_list_dotShorthand() async {
+    await assertNoDiagnostics(r'''
+enum E { a, b, c }
+
+f() {
+  List<E> a = [.a, .b, .c];
+}
+''');
+  }
+
   test_list_ok1() async {
     await assertNoDiagnostics(r'''
 f() {

pkg/linter/test/rules/omit_obvious_property_types_test.dart

@@ -203,6 +203,16 @@ class C {}
     );
   }
 
+  test_instanceCreation_nonGeneric_static_dotShorthand() async {
+    await assertNoDiagnostics(r'''
+class A {
+  static C c = .new();
+}
+
+class C {}
+''');
+  }
+
   test_instanceCreation_nonGeneric_topLevel() async {
     await assertDiagnostics(
       r'''
@@ -214,6 +224,14 @@ class C {}
     );
   }
 
+  test_instanceCreation_nonGeneric_topLevel_dotShorthand() async {
+    await assertNoDiagnostics(r'''
+C c = .new();
+
+class C {}
+''');
+  }
+
   test_list_ok1_static() async {
     await assertNoDiagnostics(r'''
 class A {