Report promise reject with no handler (behind a flag).

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index ec1941e6fd86eec42707e4d41011112961fe2109..ef628cd8151366dbed95138eb250bbfa24f46ac4 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -85,6 +85,7 @@ class ObjectOperationDescriptor;
 class ObjectTemplate;
 class Platform;
 class Primitive;
+class Promise;
 class RawOperationDescriptor;
 class Script;
 class Signature;
@@ -1236,6 +1237,12 @@ class V8_EXPORT Message {
   Local<String> GetSourceLine() const;
 
   /**
+   * Returns the promise attached to this message.  If this message has not
+   * been triggered by a promise rejection, the empty handle is returned.
+   */
+  Handle<Promise> GetPromise() const;
+
+  /**
    * Returns the origin for the script from where the function causing the
    * error originates.
    */
@@ -2817,6 +2824,7 @@ class V8_EXPORT Promise : public Object {
   Local<Promise> Chain(Handle<Function> handler);
   Local<Promise> Catch(Handle<Function> handler);
   Local<Promise> Then(Handle<Function> handler);
+  bool HasRejectHandler();
 
   V8_INLINE static Promise* Cast(Value* obj);
 
@@ -5820,7 +5828,7 @@ class Internals {
   static const int kNullValueRootIndex = 7;
   static const int kTrueValueRootIndex = 8;
   static const int kFalseValueRootIndex = 9;
-  static const int kEmptyStringRootIndex = 164;
+  static const int kEmptyStringRootIndex = 165;
 
   // The external allocation limit should be below 256 MB on all architectures
   // to avoid that resource-constrained embedders run low on memory.