Move JSSyntaxRegExp to core as a private member. This removes the last refrences to dart:coreimpl.

compiler/java/com/google/dart/compiler/DartCompiler.java

Index: compiler/java/com/google/dart/compiler/DartCompiler.java
diff --git a/compiler/java/com/google/dart/compiler/DartCompiler.java b/compiler/java/com/google/dart/compiler/DartCompiler.java
index 1d0eb2852d10b0bc68bdac262869ef47d33dd6c3..6e0b766204d0447b41e2be430aab3db9baab99bd 100644
--- a/compiler/java/com/google/dart/compiler/DartCompiler.java
+++ b/compiler/java/com/google/dart/compiler/DartCompiler.java
@@ -1180,15 +1180,6 @@ public class DartCompiler {
                                   DartCompilerListener listener) throws IOException {
     DartCompilerMainContext context = new DartCompilerMainContext(lib, provider, listener,
                                                                   config);
-    if (config.getCompilerOptions().shouldExposeCoreImpl()) {
-      if (embeddedLibraries == null) {
-        embeddedLibraries = Lists.newArrayList();
-      }
-      // use a place-holder LibrarySource instance, to be replaced when embedded
-      // in the compiler, where the dart uri can be resolved.
-      embeddedLibraries.add(new NamedPlaceHolderLibrarySource("dart:core"));
-    }
-
     new Compiler(lib, embeddedLibraries, config, context).compile();
     int errorCount = context.getErrorCount();
     if (config.typeErrorsAreFatal()) {