Fasta: Change BodyBuilder.buildCompileTimeError to throw an instance of _CompileTimeError.

This is a VM specific class that is recognized by exception handling code in VM.

Using this class instead of string guarantees that VM terminates with the correct exit code: kCompilationErrorExitCode (254) and not kErrorExitCode (255).

BUG=
R=ahe@google.com

Review-Url: https://codereview.chromium.org/2689543002 .

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -2186,7 +2186,13 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
   Expression buildCompileTimeError(error, [int charOffset = -1]) {
     String message = new InputError(uri, charOffset, error).format();
     print(message);
-    return new Throw(new StringLiteral(message));
+    // TODO(ahe): Use a method on TargetImplementation for looking up the
+    // constructor.
+    final Constructor constructor = coreTypes.getCoreClass(
+        "dart:core", "_CompileTimeError").constructors.first;
+    return new Throw(new ConstructorInvocation(
+        constructor,
+        new Arguments(<Expression>[new StringLiteral(message)])));
   }
 
   Statement buildCompileTimeErrorStatement(error, [int charOffset = -1]) {