createFragmentFromMarkupWithContext() should use EphemeralRange.

third_party/WebKit/Source/core/editing/EphemeralRange.h

Index: third_party/WebKit/Source/core/editing/EphemeralRange.h
diff --git a/third_party/WebKit/Source/core/editing/EphemeralRange.h b/third_party/WebKit/Source/core/editing/EphemeralRange.h
index 2116b2c661f26e15225db78c5dafe069f7a1cc93..c9f8883fcbb1e83e8e81863704e0be91942fcb08 100644
--- a/third_party/WebKit/Source/core/editing/EphemeralRange.h
+++ b/third_party/WebKit/Source/core/editing/EphemeralRange.h
@@ -105,6 +105,9 @@ class CORE_TEMPLATE_CLASS_EXPORT EphemeralRangeTemplate final {
   PositionTemplate<Strategy> startPosition() const;
   PositionTemplate<Strategy> endPosition() const;
 
+  Node* commonAncestorContainer() const;

[Xiaocheng, 2017/02/28 19:26:31]

Could you add unit tests for this new function?

At least two unit tests are needed, with one for DOM tree and another for flat
tree (*).

(*) https://www.w3.org/TR/shadow-dom/

[tanvir, 2017/03/02 14:59:14]

I have added the unit test cases for DOM and FlatTree.

[tanvir, 2017/03/02 14:59:14]

Done.

+  static Node* commonAncestorContainer(const Node* containerA, const Node* containerB);

[Xiaocheng, 2017/02/28 19:26:31]

There's no need to expose this function, as there's no external caller.

I think it's better to just hide it in EphemeralRange.cpp in an anonymous
namespace. You may follow the coding style in EditingUtilities.cpp

[tanvir, 2017/03/02 14:59:14]

Done.

+
   // Returns true if |m_startPositoin| == |m_endPosition| or |isNull()|.
   bool isCollapsed() const;
   bool isNull() const {