Fixes for issues

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 6347cc98683a3a15975e4e051052af1ef25d2366..c53377b25ff4a831e1e83e33dbf3c71dd850625b 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5030,6 +5030,11 @@ DART_EXPORT Dart_Handle Dart_LoadScript(Dart_Handle url,
       return result;
     }
     library ^= Library::LookupLibrary(T, resolved_url_str);
+    if (library.IsNull()) {
+      // If the URL string does not match, use the library object
+      // returned by the kernel reader.

[aam, 2017/08/24 19:20:06]

We know that this will happen when we request to load .dill file, in which case
url string, pointing to .dill file, is different from script name (by '.dill'
extension). Is there some other scenario where LookupLibrary(resolved_url_str)
returns null? Are we okay falling back to using library object returned by the
kernel reader in those cases?

[siva, 2017/08/24 23:00:42]

The scenarios when this can happen is when resolved_url_str does not match the
url string for the library objects. Currently the only known case for this is
the '.dill' extension case.

+      library ^= Api::UnwrapHandle(result);

[aam, 2017/08/25 21:56:03]

Sorry, I didn't realize that `result` here will be Dart_Null if
LoadKernelProgram at line 5028 succeeded.

[siva, 2017/08/25 21:59:47]

Good point will fix that.

+    }
     if (library.IsNull()) {
       return Api::NewError("%s: Unable to load script '%s' correctly.",
                            CURRENT_FUNC, resolved_url_str.ToCString());