Revert of Add debug checks to catch PropertyCell::cast failures.

Revert of Add debug checks to catch PropertyCell::cast failures. (patchset #1 id:1 of https://codereview.chromium.org/1025433002/)

Reason for revert:
Cause to failures found.

Original issue's description:
> Add debug checks to catch PropertyCell::cast failures.
> 
> R=verwaest@chromium.org
> 
> Committed: https://crrev.com/87af6018249a085ec99b54990ffb93c7a1148dbd
> Cr-Commit-Position: refs/heads/master@{#27309}

TBR=verwaest@chromium.org,jkummerow@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

[Yang, 2015-03-20 07:16:49]

Created Revert of Add debug checks to catch PropertyCell::cast failures.

[commit-bot: I haz the power, 2015-03-20 07:17:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021163002/1

[commit-bot: I haz the power, 2015-03-20 07:17:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-03-20 07:17:11]

Failed to apply patch for src/lookup.cc:
While running git apply --index -3 -p1;
  error: patch failed: src/lookup.cc:311
  Falling back to three-way merge...
  Applied patch to 'src/lookup.cc' with conflicts.
  U src/lookup.cc

Patch:       src/lookup.cc
Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index
2b69aa67959f957a0fc283a6b4d30892257ec081..e5eecce234116e1098c8bd23e5c2fdc6fc1bb9d0
100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -256,7 +256,6 @@
   if (holder_map_->is_dictionary_map()) {
     result = holder->property_dictionary()->ValueAt(number_);
     if (holder_map_->IsGlobalObjectMap()) {
-      DCHECK(result->IsPropertyCell());
       result = PropertyCell::cast(result)->value();
     }
   } else if (property_details_.type() == v8::internal::DATA) {
@@ -311,7 +310,6 @@
   Handle<JSObject> holder = GetHolder<JSObject>();
   Handle<GlobalObject> global = Handle<GlobalObject>::cast(holder);
   Object* value = global->property_dictionary()->ValueAt(dictionary_entry());
-  DCHECK(value->IsPropertyCell());
   return Handle<PropertyCell>(PropertyCell::cast(value));
 }