getObject now supports specifying offset,count for strings.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 20189 matching lines @@
     // special string in their program.  Fixing this involves updating
     // the debugging api a bit.
     jsobj.AddProperty("type", "Sentinel");
     jsobj.AddProperty("kind", "OptimizedOut");
     jsobj.AddProperty("valueAsString", "<optimized out>");
     return;
   }
   PrintSharedInstanceJSON(&jsobj, ref);
   jsobj.AddProperty("kind", "String");
   jsobj.AddServiceId(*this);
+  jsobj.AddProperty("length", Length());
   if (ref) {
-    bool did_truncate = jsobj.AddPropertyStr("valueAsString", *this, 128);
-    if (did_truncate) {
-      jsobj.AddProperty("valueAsStringIsTruncated", did_truncate);
+    // String refs always truncate to a fixed count;
+    const intptr_t kFixedCount = 128;
+    if (jsobj.AddPropertyStr("valueAsString", *this, 0, kFixedCount)) {
+      jsobj.AddProperty("count", kFixedCount);
+      jsobj.AddProperty("valueAsStringIsTruncated", true);
     }
-  } else {
-    bool did_truncate = jsobj.AddPropertyStr("valueAsString", *this);
-    ASSERT(!did_truncate);
+    return;
   }
+
+  intptr_t offset;
+  intptr_t count;
+  stream->ComputeOffsetAndCount(Length(), &offset, &count);
+  if (offset > 0) {
+    jsobj.AddProperty("offset", offset);
+  }
+  if (count < Length()) {
+    jsobj.AddProperty("count", count);
+  }
+  jsobj.AddPropertyStr("valueAsString", *this, offset, count);
 }
 
 
 void String::ToUTF8(uint8_t* utf8_array, intptr_t array_len) const {
   ASSERT(array_len >= Utf8::Length(*this));
   Utf8::Encode(*this, reinterpret_cast<char*>(utf8_array), array_len);
 }
 
 
 static FinalizablePersistentHandle* AddFinalizer(
@@ skipping 2608 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart