Avoid endless loop when computing line boundaries in contentEditable.

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

Index: third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp
diff --git a/third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp b/third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp
index d88be1191e520dda01cbcee7452198e8abd6a236..08e82a25cefd94ae63d1d39071bd80e47a93a837 100644
--- a/third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp
+++ b/third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp
@@ -2165,6 +2165,10 @@ void AXLayoutObject::lineBreaks(Vector<int>& lineBreaks) const
         lineBreaks.append(indexForVisiblePosition(visiblePos));
         prevVisiblePos = visiblePos;
         visiblePos = nextLinePosition(visiblePos, 0, HasEditableAXRole);
+
+        // Make sure we always make forward progress.
+        if (visiblePos.deepEquivalent().compareTo(prevVisiblePos.deepEquivalent()) < 0)
+            break;
     }
 }