When converting arguments JS->Java, handle integers correctly

Summary:
If a folly::dynamic contains a double when a Java method is
declared to take an int, getInt() will be called, and a C++ exception
will be thrown.  This change uses similar logic to
NativeReadableMap.getInt() to convert a folly::dynamic double to a
jint.  This will still throw an exception if the JS value cannot be
represented as a jint without loss.

Reviewed By: fromcelticpark

Differential Revision: D10209492

fbshipit-source-id: fd96416200c6b283ce5c8f8fa4c227ceb8f43054

ReactAndroid/src/main/jni/react/jni/MethodInvoker.cpp

@@ -49,6 +49,22 @@ jdouble extractDouble(const folly::dynamic& value) {
   }
 }
 
+jint extractInteger(const folly::dynamic& value) {
+  // The logic here is taken from convertDynamicIfIntegral, but the
+  // return type and exception are different.
+  if (value.isInt()) {
+    return value.getInt();
+  }
+  double dbl = value.getDouble();
+  jint result = static_cast<jint>(dbl);
+  if (dbl != result) {
+    throw std::invalid_argument(
+      folly::to<std::string>(
+        "Tried to convert jint argument, but got a non-integral double: ", dbl));
+  }
+  return result;
+}
+
 local_ref<JCxxCallbackImpl::jhybridobject> extractCallback(std::weak_ptr<Instance>& instance, const folly::dynamic& value) {
   if (value.isNull()) {
     return local_ref<JCxxCallbackImpl::jhybridobject>(nullptr);
@@ -101,10 +117,10 @@ jvalue extract(std::weak_ptr<Instance>& instance, char type, dynamic_iterator& i
       value.l = JBoolean::valueOf(static_cast<jboolean>(arg.getBool())).release();
       break;
     case 'i':
-      value.i = static_cast<jint>(arg.getInt());
+      value.i = extractInteger(arg);
       break;
     case 'I':
-      value.l = JInteger::valueOf(static_cast<jint>(arg.getInt())).release();
+      value.l = JInteger::valueOf(extractInteger(arg)).release();
       break;
     case 'f':
       value.f = static_cast<jfloat>(extractDouble(arg));