Reorder the functions in dart_api_impl.cc to match dart_api.h.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 1754)
+++ runtime/include/dart_api.h	(working copy)
@@ -1175,12 +1175,12 @@
 
 DART_EXPORT Dart_Handle Dart_LibraryUrl(Dart_Handle library);
 
+DART_EXPORT Dart_Handle Dart_LookupLibrary(Dart_Handle url);
+
 DART_EXPORT Dart_Handle Dart_LoadLibrary(Dart_Handle url,
                                          Dart_Handle source);
 
-DART_EXPORT Dart_Handle Dart_LookupLibrary(Dart_Handle url);
 
-
 DART_EXPORT Dart_Handle Dart_LibraryImportLibrary(Dart_Handle library,
                                                   Dart_Handle import);
 
@@ -1202,7 +1202,6 @@
     Dart_NativeEntryResolver resolver);
 // TODO(turnidge): Rename to Dart_LibrarySetNativeResolver?
 
-
 // --- Profiling support ----
 
 // External pprof support for gathering and dumping symbolic