Get rid of AX_LINE_BREAKS attribute to improve performance.

ui/accessibility/ax_node.cc

Index: ui/accessibility/ax_node.cc
diff --git a/ui/accessibility/ax_node.cc b/ui/accessibility/ax_node.cc
index a0e53fad6a25f2f6d91bd4dabc1ab238437450ee..459095eef929ad0b4aa66e1e92efda852674b993 100644
--- a/ui/accessibility/ax_node.cc
+++ b/ui/accessibility/ax_node.cc
@@ -3,6 +3,10 @@
 // found in the LICENSE file.
 
 #include "ui/accessibility/ax_node.h"
+
+#include <algorithm>
+
+#include "base/strings/string16.h"
 #include "ui/gfx/transform.h"
 
 namespace ui {
@@ -51,4 +55,33 @@ bool AXNode::IsDescendantOf(AXNode* ancestor) {
   return false;
 }
 
+std::vector<int> AXNode::GetOrComputeLineStartOffsets() {
+  std::vector<int> line_offsets;
+  if (data().GetIntListAttribute(AX_ATTR_CACHED_LINE_STARTS, &line_offsets))
+    return line_offsets;
+
+  int end_offset = 0;
+  ComputeLineStartOffsets(&line_offsets, &end_offset);
+  data_.AddIntListAttribute(AX_ATTR_CACHED_LINE_STARTS, line_offsets);
+  return line_offsets;
+}
+
+void AXNode::ComputeLineStartOffsets(std::vector<int>* line_offsets,
+                                     int* end_offset) const {
+  DCHECK(line_offsets);
+  DCHECK(end_offset);
+  for (const AXNode* child : children()) {
+    DCHECK(child);
+    if (child->child_count()) {
+      child->ComputeLineStartOffsets(line_offsets, end_offset);

[David Tseng, 2016/09/23 12:43:02]

Also, before I forget, if performance is a concern here, you could just visit
mostly only the leaves (pseudocode):
leaf = start.firstChild
while (leaf) {
  while (leaf.firstChild)
    leaf = leaf.firstChild
  visit(leaf)
  leaf = leaf.nextSibling || leaf.parent
  if (leaf == start)
    return
}

rather than visiting the entire tree recursively.

(and this leads to having possibly an incremental api, getNextLineBreakStart,
depending on re-writing the callers).

Just a note to remind us if needed.

+      continue;
+    }
+
+    base::string16 text = child->data().GetString16Attribute(ui::AX_ATTR_NAME);

[David Tseng, 2016/09/23 01:43:57]

This isn't equivalent with the way line breaks currently work in Blink. Is that
intended? Most significantly, the name here includes non-rendered content like
aria labels, images, etc. See my previous comment regarding inline textboxes.
Not sure if line breaks in Blink worked as we wanted either...

+    *end_offset += static_cast<int>(text.length());
+    if (!child->data().HasIntAttribute(ui::AX_ATTR_NEXT_ON_LINE_ID))
+      line_offsets->push_back(*end_offset);

[David Tseng, 2016/10/06 21:28:03]

This is sometimes wrong when you're on the last leaf node of a textarea or
content editable. You can't just assume there's a line break start here.

+  }
+}
+
 }  // namespace ui