Simplify the SelectorQuery constructor and reuse CSSSelectorList::length().

third_party/WebKit/Source/core/css/CSSSelectorList.h

Index: third_party/WebKit/Source/core/css/CSSSelectorList.h
diff --git a/third_party/WebKit/Source/core/css/CSSSelectorList.h b/third_party/WebKit/Source/core/css/CSSSelectorList.h
index ad7bc10d37e273383049bcaf2d401a01ad468913..3da863d4db24c4ca8d3558c899e3f446befead71 100644
--- a/third_party/WebKit/Source/core/css/CSSSelectorList.h
+++ b/third_party/WebKit/Source/core/css/CSSSelectorList.h
@@ -81,8 +81,11 @@ class CORE_EXPORT CSSSelectorList {
 
   String selectorsText() const;
 
+  // Selector lists don't know their length, computing it is O(n) and should be
+  // avoided when possible. Instead iterate from first() and using next().
+  unsigned computeLength() const;
+
  private:
-  unsigned length() const;
 
   void deleteSelectorsIfNeeded() {
     if (m_selectorArray)