Get rid of AX_LINE_BREAKS attribute to improve performance.

content/browser/accessibility/browser_accessibility.cc

Index: content/browser/accessibility/browser_accessibility.cc
diff --git a/content/browser/accessibility/browser_accessibility.cc b/content/browser/accessibility/browser_accessibility.cc
index 0797a36a0fc0c8af0e8faa15f4e5189615321aa3..575404aba2925ab160905bb769c613b097caa391 100644
--- a/content/browser/accessibility/browser_accessibility.cc
+++ b/content/browser/accessibility/browser_accessibility.cc
@@ -7,6 +7,7 @@
 #include <stddef.h>
 
 #include <algorithm>
+#include <functional>
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
@@ -533,9 +534,7 @@ int BrowserAccessibility::GetLineStartBoundary(
   DCHECK_LE(start, static_cast<int>(GetText().length()));
 
   if (IsSimpleTextControl()) {
-    const std::vector<int32_t>& line_breaks =
-        GetIntListAttribute(ui::AX_ATTR_LINE_BREAKS);
-    return ui::FindAccessibleTextBoundary(GetText(), line_breaks,
+    return ui::FindAccessibleTextBoundary(GetText(), ComputeLineBreaks(),
                                           ui::LINE_BOUNDARY, start, direction,
                                           affinity);
   }
@@ -1142,6 +1141,33 @@ std::string BrowserAccessibility::ComputeAccessibleNameFromDescendants() {
   return name;
 }
 
+std::vector<int> BrowserAccessibility::ComputeLineBreaks() const {
+  std::vector<int> line_breaks;
+  int offset = 0;
+  for (size_t i = 0; i < InternalChildCount(); ++i) {
+    const BrowserAccessibility* child = InternalGetChild(i);
+    DCHECK(child);
+    switch
+      child->GetRole() {
+        case ui::AX_ROLE_INLINE_TEXT_BOX:

[dmazzoni, 2016/09/02 15:55:00]

This algorithm is fine, it will certainly work correctly for plaintext

I think there might be a few cases where it doesn't do what we intend if you mix
content other than text into a paragraph. For example imagine you have a tiny
inline <img> element that happens to be the last thing on a line. I think you
still want to call IsNextSiblingOnSameLine() on that image even though it's not
an inline text box

So my initial thought is to just call IsNextSiblingOnSameLine on any leaf node

But I'm okay to land this and try to fix it better with AXPosition

+          offset += child->GetText().length();
+          if (!child->IsNextSiblingOnSameLine())
+            line_breaks.push_back(offset);
+          break;
+        case ui::AX_ROLE_LINE_BREAK:
+          line_breaks.push_back(offset);
+          offset += child->GetText().length();
+          break;
+        default:
+          std::vector<int> child_breaks = child->ComputeLineBreaks();
+        std::transform(child_breaks.begin(), child_breaks.end(), child_breaks.begin(), std::bind2nd()std::plus<int>, offset));

[dmazzoni, 2016/09/02 15:55:00]

Needs indentation

Could you write this using a lambda instead of bind2nd and plus? I think that'd
be more readable.

This involves a fair amount of copying, an alternative that comes to mind is to
use a helper that takes an offset argument, then you can do it all in one pass.

// Recursively finds line breaks in this subtree and appends them to the passed
vector, adding |offset| to each one.
void BrowserAccessibility::AppendLineBreaksWithOffset(int offset,
std::vector<int>* line_breaks) const {
}

std::vector<int> BrowserAccessibility::ComputeLineBreaks() const {
  std::vector<int> result;
  AppendLineBreaksWithOffset(0, &result);
  return result;
}

+        line_breaks.insert(line_breaks.end(), child_breaks.begin(),
+                           child_breaks.end());
+      }
+  }
+  return line_breaks;
+}
+
 base::string16 BrowserAccessibility::GetInnerText() const {
   if (IsTextOnlyObject())
     return GetString16Attribute(ui::AX_ATTR_NAME);