Reland: Add more API fuzzing and fix the issues encountered.

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index afaa94dc781c5288cbcb35fe0af15807254b8f53..95034108e0c01f19e2dee29e8b59508676eb0cc7 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -53,6 +53,19 @@ int64_t DartUtils::GetIntegerValue(Dart_Handle value_obj) {
 }
 
 
+bool DartUtils::GetInt64Value(Dart_Handle value_obj, int64_t* value) {
+  bool valid = Dart_IsInteger(value_obj);
+  if (valid) {
+    Dart_Handle result = Dart_IntegerFitsIntoInt64(value_obj, &valid);
+    ASSERT(!Dart_IsError(result));
+  }
+  if (!valid) return false;
+  Dart_Handle result = Dart_IntegerToInt64(value_obj, value);
+  ASSERT(!Dart_IsError(result));
+  return true;
+}
+
+
 const char* DartUtils::GetStringValue(Dart_Handle str_obj) {
   const char* cstring = NULL;
   Dart_Handle result = Dart_StringToCString(str_obj, &cstring);