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/compiler/common-operator-reducer.cc b/src/compiler/common-operator-reducer.cc
new file mode 100644
index 0000000..cf597ea
--- /dev/null
+++ b/src/compiler/common-operator-reducer.cc
@@ -0,0 +1,41 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/compiler/common-operator-reducer.h"
+
+#include "src/compiler/common-operator.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+Reduction CommonOperatorReducer::Reduce(Node* node) {
+  switch (node->opcode()) {
+    case IrOpcode::kEffectPhi:
+    case IrOpcode::kPhi: {
+      int const input_count = node->InputCount();
+      if (input_count > 1) {
+        Node* const replacement = node->InputAt(0);
+        for (int i = 1; i < input_count - 1; ++i) {
+          if (node->InputAt(i) != replacement) return NoChange();
+        }
+        return Replace(replacement);
+      }
+      break;
+    }
+    case IrOpcode::kSelect: {
+      if (node->InputAt(1) == node->InputAt(2)) {
+        return Replace(node->InputAt(1));
+      }
+      break;
+    }
+    default:
+      break;
+  }
+  return NoChange();
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8