Fix for issue 23908 - error message reports the exact error when a native extension fails to load.

runtime/bin/extensions_android.cc

 // Copyright (c) 2012, 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 "platform/assert.h"
 #include "platform/globals.h"
 #if defined(TARGET_OS_ANDROID)
 
 #include "bin/extensions.h"
 #include <dlfcn.h>  // NOLINT
 
 
 namespace dart {
 namespace bin {
 
 const char* kPrecompiledLibraryName = "libprecompiled.so";
 const char* kPrecompiledSymbolName = "_kInstructionsSnapshot";
 
-void* Extensions::LoadExtensionLibrary(const char* library_file) {
-  return dlopen(library_file, RTLD_LAZY);
+Dart_Handle Extensions::LoadExtensionLibrary(const char* library_file,
+                                             void** library_handle) {
+  ASSERT(library_handle != NULL);
+  *library_handle = dlopen(library_file, RTLD_LAZY);
+  if (*library_handle == NULL) {
+    return Dart_NewApiError(dlerror());
+  }
+  return Dart_Null();
 }
 
-void* Extensions::ResolveSymbol(void* lib_handle, const char* symbol) {
+Dart_Handle Extensions::ResolveSymbol(void* lib_handle,
+                                      const char* symbol,
+                                      void** init_function) {
+  ASSERT(init_function != NULL);
   dlerror();
-  void* result = dlsym(lib_handle, symbol);
-  if (dlerror() != NULL) return NULL;
-  return result;
+  *init_function = dlsym(lib_handle, symbol);
+  char* err_str = dlerror();

[jamesr, 2015/10/14 23:55:39]

This produces the following error in the Flutter build:

../../dart/runtime/bin/extensions_android.cc: In static member function 'static
_Dart_Handle* dart::bin::Extensions::ResolveSymbol(void*, const char*, void**)':
../../dart/runtime/bin/extensions_android.cc:39:27: error: invalid conversion
from 'const char*' to 'char*' [-fpermissive]
   char* err_str = dlerror();

the fix is to make this 'const char* err_str'.  Would it be possible for the
dart build with a higher warning level?

[siva, 2015/10/15 00:27:45]

Will fix this in the Dart repo, I thought our warnings are at the highest level
let me check that.

+  if (err_str != NULL) {
+    return Dart_NewApiError(err_str);
+  }
+  return Dart_Null();
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_ANDROID)