Oilpan: Introduce TempRangeScope to avoid needless Range attaches on Document.

Source/core/dom/Range.h

Index: Source/core/dom/Range.h
diff --git a/Source/core/dom/Range.h b/Source/core/dom/Range.h
index bb0f769176188a0d54de33ed3dabf43b39608e5b..fd653d9debce39e19f76ffe0b53b2b0d2b16faf5 100644
--- a/Source/core/dom/Range.h
+++ b/Source/core/dom/Range.h
@@ -170,6 +170,32 @@ private:
     RangeBoundaryPoint m_end;
 };
 
+#if ENABLE(OILPAN)
+// Ranges are registered on the owner document so that they can be
+// updated via the document when the document changes. Ranges are
+// often used as short-lived results of subcomputations that become
+// unreachable without any document modifications. Such short-lived
+// ranges need not be registered with the document. When a
+// TemporaryRangeScope is on the stack created range objects are not
+// attached to the document. With Oilpan this is important to not
+// build up a large set of ranges on the Document that we will waste
+// time updating even though they will never be needed.
+class TemporaryRangeScope {
+public:
+    TemporaryRangeScope() { ++s_nesting; }
+    ~TemporaryRangeScope() { --s_nesting; }
+    static bool active() { return s_nesting != 0; }

[yosin_UTC9, 2014/06/25 01:22:20]

nit: Just |return s_nesting|

+private:
+    static unsigned s_nesting;
+};
+#else
+class TemporaryRangeScope {
+public:
+    TemporaryRangeScope() { }
+    static bool active() { return false; }
+};
+#endif
+
 PassRefPtrWillBeRawPtr<Range> rangeOfContents(Node*);
 
 bool areRangesEqual(const Range*, const Range*);