Automatically applying components based on crash stacktrace and information from OWNERS files.

If this is incorrect, please apply the Test-Predator-Wrong-Components label.

Automatically assigning owner based on suspected regression changelist https://chromium.googlesource.com/chromium/src/+/7bd29404a6ab8d36bdff4123ae522fcd9068344b ([Blink] Avoid crossing editing boundaries selection.).

If this is incorrect, please let us know why and apply the Test-Predator-Wrong-CLs label. If you aren't the correct owner for this issue, please unassign yourself as soon as possible so it can be re-triaged.

Lower to Pri-3 since real world usage of InsertHorizontalRule command is low and it is caused by unusual HTML.

The root cause is using IsEditablePosition() uses Position::ParentAnchoredEquivalent() then we get
IsEditablePosition(start) = true
but HighestEditableRoot(start) = null

Where |start| is inside <hr>.

In review: http://crrev.com/c/1172273

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/53a7d96350fda4ed08c3b675c309bfb67670e2b1

commit 53a7d96350fda4ed08c3b675c309bfb67670e2b1
Author: Yoshifumi Inoue <yosin@chromium.org>
Date: Thu Aug 16 00:17:13 2018

Make IsEditablePosition() to use Position::ComputeContainerNode()

This patch changes |IsEditablePosition()| to use |Position::
ComputeContainerNode()| instead of |Position::ParentAnchoredEquivalent()| not to
incorporate |EditorIngoreContetns()|, e.g. <hr>, <img>, etc.

For "<hr contenteditable>", |IsEditablePosition(<hr>@0)| returns false before
this patch. After this patch, it returns true.

Bug:  873088 
Change-Id: Id75bd2c857dbd85e59f7795d02f3583802347060
Reviewed-on: https://chromium-review.googlesource.com/1172273
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583457}
[modify] https://crrev.com/53a7d96350fda4ed08c3b675c309bfb67670e2b1/third_party/blink/renderer/core/editing/editing_utilities.cc
[modify] https://crrev.com/53a7d96350fda4ed08c3b675c309bfb67670e2b1/third_party/blink/renderer/core/editing/editing_utilities_test.cc

ClusterFuzz has detected this issue as fixed in range 583456:583457.

Detailed report: https://clusterfuzz.com/testcase?key=6230402315059200

Fuzzer: bj_broddelwerk
Job Type: linux_asan_content_shell_drt
Platform Id: linux

Crash Type: Null-dereference READ
Crash Address: 0x000000000010
Crash State:
  blink::PositionTemplate<blink::EditingAlgorithm<blink::NodeTraversal> >::LastPos
  blink::PositionTemplate<blink::EditingAlgorithm<blink::NodeTraversal> > blink::L
  blink::LastEditablePositionBeforePositionInRoot
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=linux_asan_content_shell_drt&range=575974:575975
Fixed: https://clusterfuzz.com/revisions?job=linux_asan_content_shell_drt&range=583456:583457

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6230402315059200

See https://github.com/google/clusterfuzz-tools for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 6230402315059200 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.