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

tests/standalone/assert_test.dart

Index: tests/standalone/assert_test.dart
diff --git a/tests/standalone/assert_test.dart b/tests/standalone/assert_test.dart
index 959f992a534276025dbf4384b6266971f489d00c..8e1b288e5b28002e95553e6903e37097bdde2c11 100644
--- a/tests/standalone/assert_test.dart
+++ b/tests/standalone/assert_test.dart
@@ -10,7 +10,7 @@ class AssertTest {
     int i = 0;
     try {
       assert(false);
-    } catch (AssertionError error) {
+    } on AssertionError catch (error) {
       i = 1;
       Expect.equals("false", error.failedAssertion);
       int pos = error.url.lastIndexOf("/", error.url.length);
@@ -28,7 +28,7 @@ class AssertTest {
     int i = 0;
     try {
       assert(() => false);
-    } catch (AssertionError error) {
+    } on AssertionError catch (error) {
       i = 1;
       Expect.equals("() => false", error.failedAssertion);
       int pos = error.url.lastIndexOf("/", error.url.length);