Use RelocatablePosition in CompositeEditCommand::MoveParagraphWithClones

Clusterfuzz found a sample where
CompositeEditCommand::MoveParagraphWithClones() moves |before_paragraph|
out of the DOM tree after moving the paragraph. This patch uses
RelocatablePosition to track |before_paragraph| and |after_paragraph| so
that the positions we track are always connected.

Note: CompositeEditCommand::MoveParagraphs() is already using
RelocatablePosition to track positions before and after the moved
paragraphs.

BUG=712510
TEST=ApplyBlockElementCommandTest.IndentHeadingIntoBlockquote

Review-Url: https://codereview.chromium.org/2850773003
Cr-Commit-Position: refs/heads/master@{#468278}

third_party/WebKit/Source/core/editing/commands/ApplyBlockElementCommandTest.cpp

@@ -78,4 +78,35 @@ TEST_F(ApplyBlockElementCommandTest, visibilityChangeDuringCommand) {
       GetDocument().documentElement()->innerHTML());
 }
 
+// This is a regression test for https://crbug.com/712510
+TEST_F(ApplyBlockElementCommandTest, IndentHeadingIntoBlockquote) {
+  SetBodyContent(
+      "<div contenteditable=\"true\">"
+      "<h6><button><table></table></button></h6>"
+      "<object></object>"
+      "</div>");
+  Element* button = GetDocument().QuerySelector("button");
+  Element* object = GetDocument().QuerySelector("object");
+  Selection().SetSelection(SelectionInDOMTree::Builder()
+                               .Collapse(Position(button, 0))
+                               .Extend(Position(object, 0))
+                               .Build());
+
+  IndentOutdentCommand* command = IndentOutdentCommand::Create(
+      GetDocument(), IndentOutdentCommand::kIndent);
+  command->Apply();
+
+  // This only records the current behavior, which can be wrong.
+  EXPECT_EQ(
+      "<div contenteditable=\"true\">"
+      "<blockquote style=\"margin: 0 0 0 40px; border: none; padding: 0px;\">"
+      "<h6><button></button></h6>"
+      "<h6><button><table></table></button></h6>"
+      "</blockquote>"
+      "<h6><button></button></h6><br>"
+      "<object></object>"
+      "</div>",
+      GetDocument().body()->innerHTML());
+}
+
 }  // namespace blink

third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.cpp

@@ -1266,9 +1266,10 @@ void CompositeEditCommand::MoveParagraphWithClones(
   DCHECK(outer_node);
   DCHECK(block_element);
 
-  VisiblePosition before_paragraph =
-      PreviousPositionOf(start_of_paragraph_to_move);
-  VisiblePosition after_paragraph = NextPositionOf(end_of_paragraph_to_move);
+  RelocatablePosition relocatable_before_paragraph(
+      PreviousPositionOf(start_of_paragraph_to_move).DeepEquivalent());
+  RelocatablePosition relocatable_after_paragraph(
+      NextPositionOf(end_of_paragraph_to_move).DeepEquivalent());
 
   // We upstream() the end and downstream() the start so that we don't include
   // collapsed whitespace in the move. When we paste a fragment, spaces after
@@ -1311,14 +1312,10 @@ void CompositeEditCommand::MoveParagraphWithClones(
   // would cause 'baz' to collapse onto the line with 'foobar' unless we insert
   // a br. Must recononicalize these two VisiblePositions after the pruning
   // above.
-  // TODO(yosin): We should abort when |beforeParagraph| is a orphan when
-  // we have a sample.
-  before_paragraph = CreateVisiblePosition(before_paragraph.DeepEquivalent());
-  if (after_paragraph.IsOrphan()) {
-    editing_state->Abort();
-    return;
-  }
-  after_paragraph = CreateVisiblePosition(after_paragraph.DeepEquivalent());
+  const VisiblePosition& before_paragraph =
+      CreateVisiblePosition(relocatable_before_paragraph.GetPosition());
+  const VisiblePosition& after_paragraph =
+      CreateVisiblePosition(relocatable_after_paragraph.GetPosition());
 
   if (before_paragraph.IsNotNull() &&
       !IsDisplayInsideTable(before_paragraph.DeepEquivalent().AnchorNode()) &&