[bigint] Implement BigIntShortPrint

For an improved debugging experience.

Bug: v8:6791
Change-Id: Id4f7fea47036e4520e7b24edf34f210b664672bc
Reviewed-on: https://chromium-review.googlesource.com/699427Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48272}

src/objects.cc

@@ -3424,6 +3424,12 @@ void HeapObject::HeapObjectShortPrint(std::ostream& os) {  // NOLINT
       os << '>';
       break;
     }
+    case BIGINT_TYPE: {
+      os << "<BigInt ";
+      BigInt::cast(this)->BigIntShortPrint(os);
+      os << ">";
+      break;
+    }
     case JS_PROXY_TYPE:
       os << "<JSProxy>";
       break;

src/objects/bigint.cc

@@ -196,6 +196,17 @@ void BigInt::Initialize(int length, bool zero_initialize) {
   }
 }
 
+void BigInt::BigIntShortPrint(std::ostream& os) {
+  if (sign()) os << "-";
+  int len = length();
+  if (len == 0) {
+    os << "0";
+    return;
+  }
+  if (len > 1) os << "...";
+  os << digit(0);
+}
+
 // Private helpers for public methods.
 
 Handle<BigInt> BigInt::AbsoluteAdd(Handle<BigInt> x, Handle<BigInt> y,

src/objects/bigint.h

@@ -51,6 +51,7 @@ class BigInt : public HeapObject {
   DECL_CAST(BigInt)
   DECL_VERIFIER(BigInt)
   DECL_PRINTER(BigInt)
+  void BigIntShortPrint(std::ostream& os);
 
   // TODO(jkummerow): Do we need {synchronized_length} for GC purposes?
   DECL_INT_ACCESSORS(length)