Changes to make isolate reload functionality work with the --dfe option.

runtime/bin/loader.cc

Index: runtime/bin/loader.cc
diff --git a/runtime/bin/loader.cc b/runtime/bin/loader.cc
index 92da2ed1743262e60557a05a4b104ead1a4307fb..fb5fad38763dfa96c4e3f16ea47be065b328f18d 100644
--- a/runtime/bin/loader.cc
+++ b/runtime/bin/loader.cc
@@ -7,6 +7,7 @@
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
+#include "bin/dfe.h"
 #include "bin/extensions.h"
 #include "bin/file.h"
 #include "bin/lockers.h"
@@ -19,6 +20,10 @@ namespace bin {
 
 // Development flag.
 static bool trace_loader = false;
+#if !defined(DART_PRECOMPILED_RUNTIME)
+extern DFE dfe;
+#endif
+
 // Keep in sync with loader.dart.
 static const intptr_t _Dart_kImportExtension = 9;
 static const intptr_t _Dart_kResolveAsFilePath = 10;
@@ -638,6 +643,19 @@ Dart_Handle Loader::DartColonLibraryTagHandler(Dart_LibraryTag tag,
 Dart_Handle Loader::LibraryTagHandler(Dart_LibraryTag tag,
                                       Dart_Handle library,
                                       Dart_Handle url) {
+  if (dfe.UseDartFrontend()) {
+    Dart_Isolate current = Dart_CurrentIsolate();
+    if (!Dart_IsServiceIsolate(current) && !Dart_IsKernelIsolate(current)) {
+      // When using DFE the library tag handler should be called only when we
+      // are reloading scripts.
+      // TODO(asiva) We need to ensure that the kernel and service isolates
+      // and the spawnURI paths are always loaded from a kernel IR and do
+      // not use this path.
+      if (tag == Dart_kScriptTag) {
+        return dfe.ReloadScript(current, url);
+      }
+    }
+  }
   if (tag == Dart_kCanonicalizeUrl) {
     Dart_Handle library_url = Dart_LibraryUrl(library);
     if (Dart_IsError(library_url)) {