Tentative implementation of string slices (hidden under the flag --string-slices).

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index 29632317a5e9309ee456c2e0ce9042b0b4c48cdf..84c08dcd26dc723a20a5aab9145b1af1f382d997 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -349,6 +349,31 @@ void String::StringVerify() {
   if (IsSymbol()) {
     CHECK(!HEAP->InNewSpace(this));
   }
+  if (IsConsString()) {
+    ConsString::cast(this)->ConsStringVerify();
+  } else if (IsSlicedString()) {
+    SlicedString::cast(this)->SlicedStringVerify();
+  }
+}
+
+
+void ConsString::ConsStringVerify() {
+  CHECK(this->first()->IsString());
+  CHECK(this->second() == GetHeap()->empty_string() ||
+        this->second()->IsString());
+  CHECK(this->length() >= String::kMinNonFlatLength);
+  if (this->IsFlat()) {
+    // A flat cons can only be created by String::SlowTryFlatten.
+    // Afterwards, the first part may be externalized.
+    CHECK(this->first()->IsSeqString() || this->first()->IsExternalString());
+  }
+}
+
+
+void SlicedString::SlicedStringVerify() {
+  CHECK(!this->parent()->IsConsString());
+  CHECK(!this->parent()->IsSlicedString());
+  CHECK(this->length() >= SlicedString::kMinLength);
 }