Oilpan: Replace Node* pointers with Member<Node>s

- Make SelectorCheckerContext STACK_ALLOCATED.
- Make FocusCandidate STACK_ALLOCATED.
- Make TreeBoundaryCrossingRuleSetMap a hash map from Member<Node> to Member<CSSStyleSheetRuleSubSet>. This hash map doesn't need to be weak.

BUG=340522

Review URL: https://codereview.chromium.org/423953003

git-svn-id: svn://svn.chromium.org/blink/trunk@179087 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert of Fix SharedWorker leak when script load has failed. (https://codereview.chromium.org/424653002/)

Reason for revert:
May cause crash

Original issue's description:
> Fix SharedWorker leak when script load has failed.
> 
> When SharedWorker script load has failed and the |WebSharedWorkerImpl|
> was explicit told to terminate, the |WebSharedWorkerImpl| instance
> was never deleted.
> 
> This CL fixes the issue by invoking "delete this" when a worker thread
> instance does not exist in |stopWorkerThread()|.
> 
> TEST=fast/workers/worker-crash-with-invalid-location.html doesn't leak when --enable-leak-detection
> BUG=364390
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179011

TBR=falken@chromium.org,tkent@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=364390

Review URL: https://codereview.chromium.org/424923002

git-svn-id: svn://svn.chromium.org/blink/trunk@179088 bbb929c8-8fbe-4397-9dbb-9b2b20218538