Update V8 to version 4.1.0.21

This is a cherry-pick of all commits up to and including the
4.1.0.21 cherry-pick in Chromium.

Original commit message:

Version 4.1.0.21 (cherry-pick)

Merged 206e9136bde0f2b5ae8cb77afbb1e7833e5bd412

Unlink pages from the space page list after evacuation.

BUG=430201
LOG=N
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/953813002

Cr-Commit-Position: refs/branch-heads/4.1@{#22}
Cr-Branched-From: 2e08d2a7aa9d65d269d8c57aba82eb38a8cb0a18-refs/heads/candidates@{#25353}

---

FPIIM-449

Change-Id: I8c23c7bbb70772b4858fe8a47b64fa97ee0d1f8c
diff --git a/src/type-feedback-vector-inl.h b/src/type-feedback-vector-inl.h
index 43e768e..612004e 100644
--- a/src/type-feedback-vector-inl.h
+++ b/src/type-feedback-vector-inl.h
@@ -10,6 +10,11 @@
 namespace v8 {
 namespace internal {
 
+int TypeFeedbackVector::ic_metadata_length() const {
+  return FLAG_vector_ics ? VectorICComputer::word_count(ICSlots()) : 0;
+}
+
+
 Handle<Object> TypeFeedbackVector::UninitializedSentinel(Isolate* isolate) {
   return isolate->factory()->uninitialized_symbol();
 }
@@ -21,7 +26,7 @@
 
 
 Handle<Object> TypeFeedbackVector::PremonomorphicSentinel(Isolate* isolate) {
-  return isolate->factory()->megamorphic_symbol();
+  return isolate->factory()->premonomorphic_symbol();
 }