Fixes for issues

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "lib/stacktrace.h"
 #include "platform/assert.h"
@@ skipping 5013 matching lines @@
     if ((source == Api::Null()) || (source == NULL)) {
       RETURN_NULL_ERROR(source);
     }
     void* kernel_pgm = reinterpret_cast<void*>(source);
     result = LoadKernelProgram(T, resolved_url_str, kernel_pgm);
     if (::Dart_IsError(result)) {
       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());
     }
     I->object_store()->set_root_library(library);
     return Api::NewHandle(T, library.raw());
   }
 #endif
 
   const String& source_str = Api::UnwrapStringHandle(Z, source);
   if (source_str.IsNull()) {
@@ skipping 1655 matching lines @@
 #endif
 }
 
 DART_EXPORT void Dart_DumpNativeStackTrace(void* context) {
 #ifndef PRODUCT
   Profiler::DumpStackTrace(context);
 #endif
 }
 
 }  // namespace dart