Update almost all tests (except co19) to use the new try-catch syntax.

tests/language/string_test.dart

Index: tests/language/string_test.dart
diff --git a/tests/language/string_test.dart b/tests/language/string_test.dart
index 9cbb3e6014afbdd34b4fae11795c4d9d5a3dafa4..b8c36f36f3016d447b98339a4c146e3ce489f25c 100644
--- a/tests/language/string_test.dart
+++ b/tests/language/string_test.dart
@@ -33,7 +33,7 @@ class StringTest {
     bool exception_caught = false;
     try {
       a[1] = 12;  // Throw exception.
-    } catch (NoSuchMethodException e) {
+    } on NoSuchMethodException catch (e) {
       exception_caught = true;
     }
     Expect.equals(true, exception_caught);