Introduce ComputeTextBounds template in Range.cpp

Currently textQuads and ComputeTextRects algorithm is
mostly same. The difference of behaviour of these two functions
can be handled efficiently by using templates.

This CL is the Second patch set to achieve the above behaviour.
This CL introduces ComputeTextBounds as template function, which
will  be used by computeTextRects only in this patch.

BUG=691198

Review-Url: https://codereview.chromium.org/2839633002
Cr-Commit-Position: refs/heads/master@{#467707}

third_party/WebKit/Source/core/dom/Range.cpp

@@ -1440,7 +1440,15 @@ Node* Range::PastLastNode() const {
   return EndPosition().NodeAsRangePastLastNode();
 }
 
-static Vector<IntRect> computeTextRects(const EphemeralRange& range) {
+static void CollectAbsoluteBoundsForRange(unsigned start,
+                                          unsigned end,
+                                          const LayoutText& layout_text,
+                                          Vector<IntRect>& rects) {
+  layout_text.AbsoluteRectsForRange(rects, start, end);
+}
+
+template <typename RectType>
+static Vector<RectType> ComputeTextBounds(const EphemeralRange& range) {
   const Position& start_position = range.StartPosition();
   const Position& end_position = range.EndPosition();
   Node* const start_container = start_position.ComputeContainerNode();
@@ -1448,20 +1456,25 @@ static Vector<IntRect> computeTextRects(const EphemeralRange& range) {
   Node* const end_container = end_position.ComputeContainerNode();
   DCHECK(end_container);
 
-  Vector<IntRect> rects;
+  Vector<RectType> result;
   for (const Node& node : range.Nodes()) {
     LayoutObject* const layoutObject = node.GetLayoutObject();
     if (!layoutObject || !layoutObject->IsText())
       continue;
-    LayoutText* layout_text = ToLayoutText(layoutObject);
+    const LayoutText* layout_text = ToLayoutText(layoutObject);
     unsigned start_offset =
         node == start_container ? start_position.OffsetInContainerNode() : 0;
     unsigned end_offset = node == end_container
                               ? end_position.OffsetInContainerNode()
                               : std::numeric_limits<unsigned>::max();
-    layout_text->AbsoluteRectsForRange(rects, start_offset, end_offset);
+    CollectAbsoluteBoundsForRange(start_offset, end_offset, *layout_text,
+                                  result);
   }
-  return rects;
+  return result;
+}
+
+static Vector<IntRect> computeTextRects(const EphemeralRange& range) {
+  return ComputeTextBounds<IntRect>(range);
 }
 
 IntRect Range::BoundingBox() const {