spawnUri. Take two. This time I'll wait for Anton before committing :-).

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 7916)
+++ runtime/vm/parser.cc	(working copy)
@@ -3530,8 +3530,7 @@
 
 Dart_Handle Parser::CallLibraryTagHandler(Dart_LibraryTag tag,
                                           intptr_t token_pos,
-                                          const String& url,
-                                          const Array& import_map) {
+                                          const String& url) {
   Isolate* isolate = Isolate::Current();
   Dart_LibraryTagHandler handler = isolate->library_tag_handler();
   if (handler == NULL) {
@@ -3539,8 +3538,7 @@
   }
   Dart_Handle result = handler(tag,
                                Api::NewHandle(isolate, library_.raw()),
-                               Api::NewHandle(isolate, url.raw()),
-                               Api::NewHandle(isolate, import_map.raw()));
+                               Api::NewHandle(isolate, url.raw()));
   if (Dart_IsError(result)) {
     Error& prev_error = Error::Handle();
     prev_error ^= Api::UnwrapHandle(result);
@@ -3580,17 +3578,15 @@
     }
     ExpectToken(Token::kRPAREN);
     ExpectToken(Token::kSEMICOLON);
-    const Array& import_map = Array::Handle(library_.import_map());
     Dart_Handle handle = CallLibraryTagHandler(kCanonicalizeUrl,
                                                import_pos,
-                                               url,
-                                               import_map);
+                                               url);
     const String& canon_url = String::CheckedHandle(Api::UnwrapHandle(handle));
     // Lookup the library URL.
     Library& library = Library::Handle(Library::LookupLibrary(canon_url));
     if (library.IsNull()) {
       // Call the library tag handler to load the library.
-      CallLibraryTagHandler(kImportTag, import_pos, canon_url, import_map);
+      CallLibraryTagHandler(kImportTag, import_pos, canon_url);
       // If the library tag handler succeded without registering the
       // library we create an empty library to import.
       library = Library::LookupLibrary(canon_url);
@@ -3618,7 +3614,6 @@
 
 void Parser::ParseLibraryInclude() {
   TRACE_PARSER("ParseLibraryInclude");
-  const Array& import_map = Array::Handle(library_.import_map());
   while (CurrentToken() == Token::kSOURCE) {
     const intptr_t source_pos = token_index_;
     ConsumeToken();
@@ -3631,10 +3626,9 @@
     ExpectToken(Token::kSEMICOLON);
     Dart_Handle handle = CallLibraryTagHandler(kCanonicalizeUrl,
                                                source_pos,
-                                               url,
-                                               import_map);
+                                               url);
     const String& canon_url = String::CheckedHandle(Api::UnwrapHandle(handle));
-    CallLibraryTagHandler(kSourceTag, source_pos, canon_url, import_map);
+    CallLibraryTagHandler(kSourceTag, source_pos, canon_url);
   }
 }
 
@@ -7216,9 +7210,20 @@
 // when the script is loaded.
 RawString* Parser::ResolveImportVar(intptr_t ident_pos, const String& ident) {
   TRACE_PARSER("ResolveImportVar");
-  String& map_name = String::Handle(library_.LookupImportMap(ident));
-  if (!map_name.IsNull()) {
-    return map_name.raw();
+  const Array& import_map =
+      Array::Handle(Isolate::Current()->object_store()->import_map());
+  if (!import_map.IsNull()) {
+    intptr_t length = import_map.Length();
+    intptr_t index = 0;
+    String& name = String::Handle();
+    while (index < (length - 1)) {
+      name ^= import_map.At(index);
+      if (name.Equals(ident)) {
+        name ^= import_map.At(index + 1);
+        return name.raw();
+      }
+      index += 2;
+    }
   }
   ErrorMsg(ident_pos, "import variable '%s' has not been defined",
            ident.ToCString());