Revert of Update V8 to version 5.1.115. (patchset #1 id:1 of https://codereview.chromium.org/1783283004/ )
Revert of Update V8 to version 5.1.115. (patchset #1 id:1 of https://codereview.chromium.org/1783283004/ )

Reason for revert:
Broke compile on WebKit Linux MSAN: https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20MSAN/builds/8979

The culprit v8 CL is https://codereview.chromium.org/1783313003.

Output from failed bot:
... ../../v8/src/heap/heap.cc -o obj/v8/src/heap/v8_base.heap.o
../../v8/src/heap/heap.cc:1588:54: error: use of undeclared identifier 'size'; did you mean 'ConstantPoolEntry::size'?
    MSAN_MEMORY_IS_INITIALIZED(&entry->size_, sizeof(size));
                                                     ^~~~
                                                     ConstantPoolEntry::size
../../v8/src/msan.h:27:64: note: expanded from macro 'MSAN_MEMORY_IS_INITIALIZED'
#define MSAN_MEMORY_IS_INITIALIZED(p, s) __msan_unpoison((p), (s))
                                                               ^
../../v8/src/assembler.h:1222:14: note: 'ConstantPoolEntry::size' declared here
  static int size(Type type) {
             ^
../../v8/src/heap/heap.cc:1588:53: error: invalid application of 'sizeof' to a function type
    MSAN_MEMORY_IS_INITIALIZED(&entry->size_, sizeof(size));
                                                    ^~~~~~
../../v8/src/msan.h:27:64: note: expanded from macro 'MSAN_MEMORY_IS_INITIALIZED'
#define MSAN_MEMORY_IS_INITIALIZED(p, s) __msan_unpoison((p), (s))
                                                               ^
../../v8/src/heap/heap.cc:1589:53: error: use of undeclared identifier 'obj'
    MSAN_MEMORY_IS_INITIALIZED(&entry->obj_, sizeof(obj));

Original issue's description:
> Update V8 to version 5.1.115.
>
> Summary of changes available at:
> https://chromium.googlesource.com/v8/v8/+log/a09b4096..235b98f3
>
> Please follow these instructions for assigning/CC'ing issues:
> https://github.com/v8/v8/wiki/Triaging%20issues
>
> Please close rolling in case of a roll revert:
> https://v8-roll.appspot.com/
> This only works with a Google account.
>
> TBR=hablich@chromium.org,machenbach@chromium.org,yangguo@chromium.org,vogelheim@chromium.org
>
> Committed: https://crrev.com/15e94e2a8ea96963f9638f1abec11d4eb55869c8
> Cr-Commit-Position: refs/heads/master@{#380727}

TBR=hablich@chromium.org,machenbach@chromium.org,vogelheim@chromium.org,yangguo@chromium.org,v8-autoroll@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1788763004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#380743}

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