Fix VM implementation of CastError not to extend TypeError (issue 5280).

tests/language/type_cast_vm_test.dart

Index: tests/language/type_cast_vm_test.dart
===================================================================
--- tests/language/type_cast_vm_test.dart	(revision 25753)
+++ tests/language/type_cast_vm_test.dart	(working copy)
@@ -22,12 +22,12 @@
     int result = 0;
     try {
       var i = "hello" as int;  // Throws a CastError
-    } on TypeError catch (error, stacktrace) {
+    } catch (error, stacktrace) {
       result = 1;
       Expect.isTrue(error is CastError);
-      Expect.equals("int", error.dstType);
-      Expect.equals("String", error.srcType);
-      Expect.equals("type cast", error.dstName);
+      var msg = error.toString();
+      Expect.isTrue(msg.contains("int"));  // dstType
+      Expect.isTrue(msg.contains("String"));  // srcType
       checkTopFunction("type_cast_vm_test.dart:24:23", stacktrace);
     }
     return result;
@@ -44,7 +44,7 @@
       a[0] = 0;
       a[index()]++;  // Type check succeeds, but does not create side effects.
       Expect.equals(1, a[0]);
-    } on TypeError catch (error) {
+    } catch (error) {
       result = 100;
     }
     return result;
@@ -57,12 +57,12 @@
     }
     try {
       int i = f("hello" as int);  // Throws a CastError
-    } on TypeError catch (error, stacktrace) {
+    } catch (error, stacktrace) {
       result = 1;
       Expect.isTrue(error is CastError);
-      Expect.equals("int", error.dstType);
-      Expect.equals("String", error.srcType);
-      Expect.equals("type cast", error.dstName);
+      var msg = error.toString();
+      Expect.isTrue(msg.contains("int"));  // dstType
+      Expect.isTrue(msg.contains("String"));  // srcType
       checkTopFunction("type_cast_vm_test.dart:59:25", stacktrace);
     }
     return result;
@@ -75,12 +75,12 @@
     }
     try {
       int i = f("hello");
-    } on TypeError catch (error, stacktrace) {
+    } catch (error, stacktrace) {
       result = 1;
       Expect.isTrue(error is CastError);
-      Expect.equals("int", error.dstType);
-      Expect.equals("String", error.srcType);
-      Expect.equals("type cast", error.dstName);
+      var msg = error.toString();
+      Expect.isTrue(msg.contains("int"));  // dstType
+      Expect.isTrue(msg.contains("String"));  // srcType
       checkTopFunction("type_cast_vm_test.dart:74:16", stacktrace);
     }
     return result;
@@ -93,11 +93,11 @@
     Expect.equals(5, (field as String).length);
     try {
       field as int;  // Throws a CastError
-    } on TypeError catch (error, stacktrace) {
+    } catch (error, stacktrace) {
       result = 1;
-      Expect.equals("int", error.dstType);
-      Expect.equals("String", error.srcType);
-      Expect.equals("type cast", error.dstName);
+      var msg = error.toString();
+      Expect.isTrue(msg.contains("int"));  // dstType
+      Expect.isTrue(msg.contains("String"));  // srcType
       checkTopFunction("type_cast_vm_test.dart:95:13", stacktrace);
     }
     return result;
@@ -111,11 +111,11 @@
     anyFunction = null as Function;  // No error.
     try {
       var i = f as int;  // Throws a TypeError if type checks are enabled.
-    } on TypeError catch (error, stacktrace) {
+    } catch (error, stacktrace) {
       result = 1;
-      Expect.equals("int", error.dstType);
-      Expect.equals("() => dynamic", error.srcType);
-      Expect.equals("type cast", error.dstName);
+      var msg = error.toString();
+      Expect.isTrue(msg.contains("int"));  // dstType
+      Expect.isTrue(msg.contains("() => dynamic"));  // srcType
       checkTopFunction("type_cast_vm_test.dart:113:17", stacktrace);
     }
     return result;