Implements selection behavior that determines how AXRange is mapped to a DOM range

Still preliminary until patches implementing tree ordering operators on AXObject and support for aria-labels and alt text positions are in.
R=dmazzoni@chromium.org

Change-Id: Ia19131b53d8a20d299a431695641b11ddc805280
Reviewed-on: https://chromium-review.googlesource.com/954182
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547299}

third_party/WebKit/Source/modules/accessibility/AXPosition.cpp

@@ -223,11 +223,41 @@ bool AXPosition::IsTextPosition() const {
   return IsValid() && container_object_->GetNode()->IsTextNode();
 }
 
-const PositionWithAffinity AXPosition::ToPositionWithAffinity() const {
+const AXPosition AXPosition::CreateNextPosition() const {
+  if (IsTextPosition()) {
+    if (!ContainerObject()->NextInTreeObject())
+      return {};
+    return CreatePositionBeforeObject(*ContainerObject()->NextInTreeObject());
+  }
+
+  if (!ObjectAfterPosition())
+    return {};
+  return CreatePositionBeforeObject(*ObjectAfterPosition());
+}
+
+const AXPosition AXPosition::CreatePreviousPosition() const {
+  if (!ContainerObject()->PreviousInTreeObject())
+    return {};
+  return CreatePositionAfterObject(*ContainerObject()->PreviousInTreeObject());
+}
+
+const PositionWithAffinity AXPosition::ToPositionWithAffinity(
+    const AXPositionAdjustmentBehavior adjustment_behavior) const {
   if (!IsValid())
     return {};
 
   const Node* container_node = container_object_->GetNode();
+  if (!container_node) {
+    switch (adjustment_behavior) {
+      case AXPositionAdjustmentBehavior::kMoveRight:
+        CreateNextPosition().ToPositionWithAffinity(adjustment_behavior);
+        break;
+      case AXPositionAdjustmentBehavior::kMoveLeft:
+        CreatePreviousPosition().ToPositionWithAffinity(adjustment_behavior);
+        break;
+    }
+  }
+
   if (!IsTextPosition()) {
     if (ChildIndex() ==
         static_cast<int>(container_object_->Children().size())) {

third_party/WebKit/Source/modules/accessibility/AXPosition.h

@@ -20,6 +20,11 @@ namespace blink {
 
 class AXObject;
 
+// When converting to a DOM position from an |AXPosition| and the corresponding
+// DOM position is invalid or doesn't exist, determines how to adjust the
+// |AXPosition| in order to make it valid.
+enum class AXPositionAdjustmentBehavior { kMoveLeft, kMoveRight };
+
 // Describes a position in the Blink accessibility tree.
 // A position is either anchored to before or after a child object inside a
 // container object, or is anchored to a character inside a text object.
@@ -58,7 +63,12 @@ class MODULES_EXPORT AXPosition final {
   // object.
   bool IsTextPosition() const;
 
-  const PositionWithAffinity ToPositionWithAffinity() const;
+  const AXPosition CreateNextPosition() const;
+  const AXPosition CreatePreviousPosition() const;
+
+  const PositionWithAffinity ToPositionWithAffinity(
+      const AXPositionAdjustmentBehavior =
+          AXPositionAdjustmentBehavior::kMoveLeft) const;
 
  private:
   AXPosition();

third_party/WebKit/Source/modules/accessibility/AXSelection.cpp

@@ -94,12 +94,38 @@ bool AXSelection::IsValid() const {
   return true;
 }
 
-const SelectionInDOMTree AXSelection::AsSelection() const {
+const SelectionInDOMTree AXSelection::AsSelection(
+    const AXSelectionBehavior selection_behavior) const {
   if (!IsValid())
     return {};
 
-  const auto dom_base = base_.ToPositionWithAffinity();
-  const auto dom_extent = extent_.ToPositionWithAffinity();
+  AXPositionAdjustmentBehavior base_adjustment =
+      AXPositionAdjustmentBehavior::kMoveLeft;
+  AXPositionAdjustmentBehavior extent_adjustment =
+      AXPositionAdjustmentBehavior::kMoveLeft;
+  switch (selection_behavior) {
+    case AXSelectionBehavior::kShrinkToValidDOMRange:
+      if (base_ <= extent_) {
+        base_adjustment = AXPositionAdjustmentBehavior::kMoveRight;
+        extent_adjustment = AXPositionAdjustmentBehavior::kMoveLeft;
+      } else {
+        base_adjustment = AXPositionAdjustmentBehavior::kMoveLeft;
+        extent_adjustment = AXPositionAdjustmentBehavior::kMoveRight;
+      }
+      break;
+    case AXSelectionBehavior::kExtendToValidDOMRange:
+      if (base_ <= extent_) {
+        base_adjustment = AXPositionAdjustmentBehavior::kMoveLeft;
+        extent_adjustment = AXPositionAdjustmentBehavior::kMoveRight;
+      } else {
+        base_adjustment = AXPositionAdjustmentBehavior::kMoveRight;
+        extent_adjustment = AXPositionAdjustmentBehavior::kMoveLeft;
+      }
+      break;
+  }
+
+  const auto dom_base = base_.ToPositionWithAffinity(base_adjustment);
+  const auto dom_extent = extent_.ToPositionWithAffinity(extent_adjustment);
   SelectionInDOMTree::Builder selection_builder;
   selection_builder.SetBaseAndExtent(dom_base.GetPosition(),
                                      dom_extent.GetPosition());
@@ -107,13 +133,13 @@ const SelectionInDOMTree AXSelection::AsSelection() const {
   return selection_builder.Build();
 }
 
-void AXSelection::Select() {
+void AXSelection::Select(const AXSelectionBehavior selection_behavior) {
   if (!IsValid()) {
     NOTREACHED();
     return;
   }
 
-  const SelectionInDOMTree selection = AsSelection();
+  const SelectionInDOMTree selection = AsSelection(selection_behavior);
   DCHECK(selection.AssertValid());
   Document* document = selection.Base().GetDocument();
   if (!document) {

third_party/WebKit/Source/modules/accessibility/AXSelection.h

@@ -16,6 +16,15 @@
 
 namespace blink {
 
+// If the |AXSelection| is defined by endpoints that are present in the
+// accessibility tree but not in the DOM tree, determines whether setting the
+// selection will shrink or extend the |AXSelection| to encompass endpoints that
+// are in the DOM.
+enum class AXSelectionBehavior {
+  kShrinkToValidDOMRange,
+  kExtendToValidDOMRange
+};
+
 class MODULES_EXPORT AXSelection final {
   DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 
@@ -33,10 +42,13 @@ class MODULES_EXPORT AXSelection final {
   // invalid, or if the positions are in two separate documents.
   bool IsValid() const;
 
-  const SelectionInDOMTree AsSelection() const;
+  const SelectionInDOMTree AsSelection(
+      const AXSelectionBehavior =
+          AXSelectionBehavior::kExtendToValidDOMRange) const;
 
   // Tries to set the DOM selection to this.
-  void Select();
+  void Select(
+      const AXSelectionBehavior = AXSelectionBehavior::kExtendToValidDOMRange);
 
  private:
   AXSelection();