Add a class comment to LayoutText

Source/core/layout/LayoutText.h

Index: Source/core/layout/LayoutText.h
diff --git a/Source/core/layout/LayoutText.h b/Source/core/layout/LayoutText.h
index 155e94f12ffc32e402f961032a4a0dea535c713b..7d31eab7ba56475cfacafb66387302bd36a36100 100644
--- a/Source/core/layout/LayoutText.h
+++ b/Source/core/layout/LayoutText.h
@@ -37,6 +37,20 @@ namespace blink {
 class AbstractInlineTextBox;
 class InlineTextBox;
 
+// LayoutText is the root class for anything that represents
+// a text node (see core/dom/Text.h).
+//
+// To limit memory overhead, this class inherits directly
+// from LayoutObject. It also means that it's mostly a
+// placeholder in the tree for the text node's content and
+// the line boxes.
+//
+// The actual layout of text is handled by the containing inline
+// or block flow, that will invoke the bidi algorithm to break the
+// text into lines (m_firstTextBox and m_lastTextBox).
+// See e.g. LayoutBlockFlow::layoutInlineChildren.

[eae, 2015/08/27 22:22:25]

It is probably worth pointing out that this class does contain the logic for
prefs width calculation so it's more than just a placeholder.

+//
+// The previous comment applies also for painting.
 class CORE_EXPORT LayoutText : public LayoutObject {
 public:
     // FIXME: If the node argument is not a Text node or the string argument is
@@ -171,6 +185,7 @@ private:
     // callers with a LayoutObject* can continue to use length().
     unsigned length() const final { return textLength(); }
 
+    // See the class comment as to why we shouldn't call this function directly.
     void paint(const PaintInfo&, const LayoutPoint&) final { ASSERT_NOT_REACHED(); }
     void layout() final { ASSERT_NOT_REACHED(); }
     bool nodeAtPoint(HitTestResult&, const HitTestLocation&, const LayoutPoint&, HitTestAction) final { ASSERT_NOT_REACHED(); return false; }