Remove SVGElementRareData::owner_

This appears to have been dead/unused since the complicated weak
handling for SVGCursorElement was removed in
https://codereview.chromium.org/2522443002 (together with
SVGCursorElement itself.)

Simplify SVGElement::EnsureSVGRareData a little while at it.

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I0e29e2830bc20fd595d41d72eb9c3ec23c2df2ce
Reviewed-on: https://chromium-review.googlesource.com/843023Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#526071}

third_party/WebKit/Source/core/svg/SVGElement.cpp

@@ -119,10 +119,8 @@ void SVGElement::BuildPendingResourcesIfNeeded() {
 }
 
 SVGElementRareData* SVGElement::EnsureSVGRareData() {
-  if (HasSVGRareData())
-    return SvgRareData();
-
-  svg_rare_data_ = new SVGElementRareData(this);
+  if (!svg_rare_data_)
+    svg_rare_data_ = new SVGElementRareData();
   return svg_rare_data_.Get();
 }
 

third_party/WebKit/Source/core/svg/SVGElementRareData.cpp

@@ -45,7 +45,6 @@ void SVGElementRareData::Trace(blink::Visitor* visitor) {
   visitor->Trace(animated_smil_style_properties_);
   visitor->Trace(element_instances_);
   visitor->Trace(corresponding_element_);
-  visitor->Trace(owner_);
 }
 
 AffineTransform* SVGElementRareData::AnimateMotionTransform() {

third_party/WebKit/Source/core/svg/SVGElementRareData.h

@@ -34,9 +34,8 @@ class SVGElementProxySet;
 class SVGElementRareData
     : public GarbageCollectedFinalized<SVGElementRareData> {
  public:
-  SVGElementRareData(SVGElement* owner)
-      : owner_(owner),
-        corresponding_element_(nullptr),
+  SVGElementRareData()
+      : corresponding_element_(nullptr),
         instances_updates_blocked_(false),
         use_override_computed_style_(false),
         needs_override_computed_style_update_(false),
@@ -103,7 +102,6 @@ class SVGElementRareData
   void Trace(blink::Visitor*);
 
  private:
-  Member<SVGElement> owner_;
   SVGElementSet outgoing_references_;
   SVGElementSet incoming_references_;
   HeapHashSet<WeakMember<SVGElement>> element_instances_;