Revert "Fix retargeting of result in elementFromPoint and elementsFromPoint"

This reverts commit dd944882a245a5117b50cb417138d92f32d931d6.

Reason for revert:
This causes WebKit Linux Trusty ASAN buildbot failure.
https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Linux%20Trusty%20ASAN/builds/8618

23:46:29.565 3877   ==1==ERROR: AddressSanitizer: use-after-poison on address 0x7ead60c0dbf0 at pc 0x00000dca937a bp 0x7ffd86b90c10 sp 0x7ffd86b90c08
23:46:29.565 3877   READ of size 8 at 0x7ead60c0dbf0 thread T0 (content_shell)
23:46:29.565 3877       #0 0xdca9379 in operator==<const blink::TreeScope, const blink::TreeScope> third_party/WebKit/Source/platform/heap/Member.h:128:27
23:46:29.565 3877       #1 0xdca9379 in blink::TreeScope::Retarget(blink::Element const&) const third_party/WebKit/Source/core/dom/TreeScope.cpp:393:0
23:46:29.565 3877       #2 0xdca8894 in blink::TreeScope::HitTestPointInternal(blink::Node*) const third_party/WebKit/Source/core/dom/TreeScope.cpp:267:10
23:46:29.565 3877       #3 0xdca8325 in HitTestPoint third_party/WebKit/Source/core/dom/TreeScope.cpp:254:10
23:46:29.566 3877       #4 0xdca8325 in blink::TreeScope::ElementFromPoint(double, double) const third_party/WebKit/Source/core/dom/TreeScope.cpp:245:0
23:46:29.566 3877       #5 0xc9353a7 in elementFromPoint third_party/WebKit/Source/core/dom/DocumentOrShadowRoot.h:38:23

Original change's description:
> Fix retargeting of result in elementFromPoint and elementsFromPoint
>
> Currently elementFromPoint and elementsFromPoint are not per spec, and it may
> return null incorrectly. This change adds retargeting of the result with
> respect to the context object, and adds some tests that are similar to
> elementFromPoint tests in WebKit, but with some corrected cases:
> https://git.webkit.org/?p=WebKit-https.git;a=blob;f=LayoutTests/fast/shadow-dom/DocumentOrShadowRoot-prototype-elementFromPoint.html;h=a8dc4da2430713521b9ba77c742db10397a8e638;hb=HEAD
>
> Spec:
> https://w3c.github.io/webcomponents/spec/shadow/#extensions-to-the-documentorshadowroot-mixin
>
> Bug: 759947
> Change-Id: I6aece5e9cc826124772c6ce13c806865055b2b9b
> Reviewed-on: https://chromium-review.googlesource.com/808446
> Commit-Queue: Rakina Zata Amni <[email protected]>
> Reviewed-by: Dmitry Gozman <[email protected]>
> Reviewed-by: Hayato Ito <[email protected]>
> Reviewed-by: Takayoshi Kochi <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#531139}

[email protected],[email protected],[email protected],[email protected],[email protected]

Change-Id: Id62abd371d93627d3178b63ca189cecfe9ff44d4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 759947
Reviewed-on: https://chromium-review.googlesource.com/880264
Reviewed-by: Takashi Sakamoto <[email protected]>
Commit-Queue: Takashi Sakamoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#531178}

Author: tasak