It's an unnecessary class that is complicating the line box hierarchy. It needs to go.
Created attachment 50620 [details] Patch to remove InlineRunBox
Attachment 50620 [details] did not pass style-queue: Failed to run "WebKitTools/Scripts/check-webkit-style" exit_code: 1 WARNING: Could not read file. Skipping: "WebCore/rendering/InlineRunBox.h" WebCore/rendering/RenderLineBoxList.cpp:324: Tests for true/false, null/non-null, and zero/non-zero should all be done without equality comparisons. [readability/comparison_to_zero] [5] WebCore/rendering/InlineFlowBox.h:176: One space before end of line comments [whitespace/comments] [5] WebCore/rendering/InlineFlowBox.h:177: One space before end of line comments [whitespace/comments] [5] WebCore/rendering/InlineTextBox.h:123: One space before end of line comments [whitespace/comments] [5] WebCore/rendering/InlineTextBox.h:124: One space before end of line comments [whitespace/comments] [5] Total errors found: 5 in 17 files If any of these errors are false positives, please file a bug against check-webkit-style.
Fixed in r55928.