Attempt at pre-calculating replace regexp matches.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 4cc9b9f8340238549a12136218672eb205771007..33f89439e64aeb40d768df69a97393512cfa9cbe 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -3025,6 +3025,38 @@ void Map::ClearCodeCache() {
 }
 
 
+void JSArray::Resize(int required_size) {
+  ASSERT(HasFastElements());
+  int current_length = Smi::cast(this->length())->value();
+  Array* elts = elements();
+  if (required_size < current_length) {
+    // Set length before potentially expanding. If a new backing array is
+    // allocated, we will only copy the data below the new length.
+    this->set_length(Smi::FromInt(required_size));
+  }
+  const int kArraySizeThatFitsComfortablyInNewSpace = 128;
+  if (elts->length() < required_size) {
+    // Doubling in size would be overkill, but leave some slack to avoid
+    // constantly growing.
+    Expand(required_size + (required_size >> 3));
+    // It's a performance benefit to keep a frequently used array in new-space.
+  } else if (!Heap::InNewSpace(elts) &&
+             required_size < kArraySizeThatFitsComfortablyInNewSpace) {
+    // Expand will allocate a new backing store in new space even if the size
+    // we asked for isn't larger than what we had before.
+    Expand(required_size);
+  } else {
+    // Using same backing store.
+    if (current_length > required_size) {
+      for (int i = required_size; i < current_length; i++) {
+        FixedArray::cast(elts)->set_the_hole(i);
+      }
+      return;
+    }
+  }
+}
+
+
 void JSArray::EnsureSize(int required_size) {
   ASSERT(HasFastElements());
   Array* elts = elements();