SVG: Add comment to |loopbreaker| local static var that it is safe

Source/core/svg/animation/SVGSMILElement.cpp

Index: Source/core/svg/animation/SVGSMILElement.cpp
diff --git a/Source/core/svg/animation/SVGSMILElement.cpp b/Source/core/svg/animation/SVGSMILElement.cpp
index 3a914e8d23c01755a6d61dc60287753ed5350176..f15005ddae124af748cbb134ab13b7d3a102f91f 100644
--- a/Source/core/svg/animation/SVGSMILElement.cpp
+++ b/Source/core/svg/animation/SVGSMILElement.cpp
@@ -1247,6 +1247,9 @@ bool SVGSMILElement::progress(SMILTime elapsed, SVGSMILElement* resultElement, b
 void SVGSMILElement::notifyDependentsIntervalChanged()
 {
     ASSERT(m_intervalBegin.isFinite());
+    // |loopbreaker| is used to avoid infinite recursions which may be caused from:

[haraken, 2014/05/30 01:39:45]

loopBreaker

+    // |notifyDependentsIntervalChanged| -> |createInstanceTimesFromSyncbase| -> |add{Begin,End}Time| -> |{begin,end}TimeChanged| -> |notifyDependentsIntervalChanged|
+    // |loopbreaker| is defined as a Persistent<HeapHashSet<Member<SVGSMILElement> > >. This is safe because it is guaranteed to be empty after the root |notifyDependentsIntervalChanged| has exit.

[haraken, 2014/05/30 01:39:45]

this is safe => this won't cause leaks
has exit => has exited

     DEFINE_STATIC_LOCAL(OwnPtrWillBePersistent<WillBeHeapHashSet<RawPtrWillBeMember<SVGSMILElement> > >, loopBreaker, (adoptPtrWillBeNoop(new WillBeHeapHashSet<RawPtrWillBeMember<SVGSMILElement> >())));
     if (!loopBreaker->add(this).isNewEntry)
         return;