[vm] Revise Dart_IntegerToHexCString to avoid dependency on Bigint

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index c5faed86ee98228f863825674ed14900e357236c..42775308757f8bf7bd14446a07ef7569ba056387 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -18238,6 +18238,16 @@ RawInteger* Integer::AsValidInteger() const {
   return raw();
 }
 
+const char* Integer::ToHexCString(Zone* zone) const {
+  ASSERT(IsSmi() || IsMint());  // Bigint has its own implementation.
+  int64_t value = AsInt64Value();
+  if (value < 0) {
+    return OS::SCreate(zone, "-0x%" PRIX64, static_cast<uint64_t>(-value));

[zra, 2017/08/01 16:21:57]

We have some abbreviations for these here:

https://github.com/dart-lang/sdk/blob/master/runtime/platform/globals.h#L390

Also, I think they have to be followed by "", so:

OS::SCreate(zone, "-0x%" Px64 "", ...)

[alexmarkov, 2017/08/01 17:40:11]

Introduced new short form specifier PX64, see
https://codereview.chromium.org/2985423002/
I think there is no need in trailing "", because these format specifier
constants are just string literals like "d" or "llx". Can you clarify why
appending an empty string at the end is useful?

+  } else {
+    return OS::SCreate(zone, "0x%" PRIX64, static_cast<uint64_t>(value));
+  }
+}
+
 RawInteger* Integer::ArithmeticOp(Token::Kind operation,
                                   const Integer& other,
                                   Heap::Space space) const {