Empty inline elements always get a line box.

Source/core/rendering/line/BreakingContextInlineHeaders.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All right reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 401 matching lines @@
     return false;
 }
 
 inline void BreakingContext::handleEmptyInline()
 {
     // This should only end up being called on empty inlines
     ASSERT(isEmptyInline(m_current.object()));
 
     RenderInline* flowBox = toRenderInline(m_current.object());
 
-    // Now that some inline flows have line boxes, if we are already ignoring spaces, we need
-    // to make sure that we stop to include this object and then start ignoring spaces again.
-    // If this object is at the start of the line, we need to behave like list markers and
-    // start ignoring spaces.
     bool requiresLineBox = alwaysRequiresLineBox(m_current.object());
     if (requiresLineBox || requiresLineBoxForContent(flowBox, m_lineInfo)) {
-        // An empty inline that only has line-height, vertical-align or font-metrics will only get a
-        // line box to affect the height of the line if the rest of the line is not empty.
+        // An empty inline that only has line-height, vertical-align or font-metrics will
+        // not force linebox creation (and thus affect the height of the line) if the rest of the line is empty.
         if (requiresLineBox)
             m_lineInfo.setEmpty(false, m_block, &m_width);
         if (m_ignoringSpaces) {
+            // If we are in a run of ignored spaces then ensure we get a linebox if lineboxes are eventually
+            // created for the line...
             m_trailingObjects.clear();
             m_lineMidpointState.ensureLineBoxInsideIgnoredSpaces(m_current.object());
+        } else if (m_currentCharacterIsSpace) {
+            // .. likewise if we come after a single space.
+            m_lineMidpointState.ensureLineBoxForRenderer(m_current.object());
         } else if (m_blockStyle->collapseWhiteSpace() && m_resolver.position().object() == m_current.object()
             && shouldSkipWhitespaceAfterStartObject(m_block, m_current.object(), m_lineMidpointState)) {
-            // Like with list markers, we start ignoring spaces to make sure that any
-            // additional spaces we see will be discarded.
+            // If this object is at the start of the line, we need to behave like list markers and
+            // start ignoring spaces.
             m_currentCharacterShouldCollapseIfPreWap = m_currentCharacterIsSpace = true;
             m_ignoringSpaces = true;
         }
     }
 
     m_width.addUncommittedWidth((inlineLogicalWidth(m_current.object()) + borderPaddingMarginStart(flowBox) + borderPaddingMarginEnd(flowBox)).toFloat());
 }
 
 inline void BreakingContext::handleReplaced()
 {
@@ skipping 456 matching lines @@
 
     if (style->textIndentType() == TextIndentHanging)
         shouldIndentText = shouldIndentText == IndentText ? DoNotIndentText : IndentText;
 
     return shouldIndentText;
 }
 
 }
 
 #endif // BreakingContextInlineHeaders_h