Provide better error messages when we fail to build the builtin lib.

runtime/bin/builtin_in.cc

Index: runtime/bin/builtin_in.cc
===================================================================
--- runtime/bin/builtin_in.cc	(revision 1553)
+++ runtime/bin/builtin_in.cc	(working copy)
@@ -74,7 +74,7 @@
                                          int argument_count) {
   const char* function_name = NULL;
   Dart_Handle result = Dart_StringToCString(name, &function_name);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
   ASSERT(function_name != NULL);
   int num_entries = sizeof(BuiltinEntries) / sizeof(struct NativeEntries);
   for (int i = 0; i < num_entries; i++) {
@@ -104,21 +104,21 @@
   // Load the library.
   Dart_Handle source = Dart_NewString(Builtin_source_);
   Dart_Handle builtin_lib = Dart_LoadLibrary(url, source);
-  ASSERT(!Dart_IsError(builtin_lib));
+  DART_CHECK_VALID(builtin_lib);
 
   // Lookup the core libraries and inject the builtin library into them.
   Dart_Handle core_lib = Dart_LookupLibrary(Dart_NewString("dart:core"));
-  ASSERT(!Dart_IsError(core_lib));
+  DART_CHECK_VALID(core_lib);
   result = Dart_LibraryImportLibrary(core_lib, builtin_lib);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
 
   Dart_Handle coreimpl_lib =
       Dart_LookupLibrary(Dart_NewString("dart:coreimpl"));
-  ASSERT(!Dart_IsError(coreimpl_lib));
+  DART_CHECK_VALID(coreimpl_lib);
   result = Dart_LibraryImportLibrary(coreimpl_lib, builtin_lib);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
   result = Dart_LibraryImportLibrary(builtin_lib, coreimpl_lib);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
 
   // Create a native wrapper "EventHandlerNativeWrapper" so that we can add a
   // native field to store the event handle for implementing all
@@ -128,7 +128,7 @@
   result = Dart_CreateNativeWrapperClass(builtin_lib,
                                          name,
                                          kNumEventHandlerFields);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
 }
 
 
@@ -137,16 +137,16 @@
 
   Dart_Handle url = Dart_NewString(DartUtils::kBuiltinLibURL);
   Dart_Handle builtin_lib = Dart_LookupLibrary(url);
-  ASSERT(!Dart_IsError(builtin_lib));
+  DART_CHECK_VALID(builtin_lib);
   Dart_Handle result = Dart_LibraryImportLibrary(library, builtin_lib);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
 }
 
 
 void Builtin_SetNativeResolver() {
   Dart_Handle url = Dart_NewString(DartUtils::kBuiltinLibURL);
   Dart_Handle builtin_lib = Dart_LookupLibrary(url);
-  ASSERT(!Dart_IsError(builtin_lib));
+  DART_CHECK_VALID(builtin_lib);
   Dart_Handle result = Dart_SetNativeResolver(builtin_lib, native_lookup);
-  ASSERT(!Dart_IsError(result));
+  DART_CHECK_VALID(result);
 }