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

tests/language/null_pointer_exception_test.dart

Index: tests/language/null_pointer_exception_test.dart
diff --git a/tests/language/null_pointer_exception_test.dart b/tests/language/null_pointer_exception_test.dart
index 64d5d3956c8f8b3576fb36e172f4ff98e42da2ec..0872cead17a95c68d4e99b139bef1c9cee059326 100644
--- a/tests/language/null_pointer_exception_test.dart
+++ b/tests/language/null_pointer_exception_test.dart
@@ -10,9 +10,9 @@ class NullPointerExceptionTest {
     bool wrongExceptionCaught = false;
     try {
       variable++;
-    } catch (NullPointerException ex) {
+    } on NullPointerException catch (ex) {
       exceptionCaught = true;
-    } catch (Exception ex) {
+    } on Exception catch (ex) {
       wrongExceptionCaught = true;
     }
     Expect.equals(true, exceptionCaught);
@@ -29,9 +29,9 @@ class NullPointerExceptionTest {
     bool wrongExceptionCaught = false;
     try {
       variable = helperFunction(variable);
-    } catch (NullPointerException ex) {
+    } on NullPointerException catch (ex) {
       exceptionCaught = true;
-    } catch (Exception ex) {
+    } on Exception catch (ex) {
       wrongExceptionCaught = true;
     }
     Expect.equals(true, exceptionCaught);