Make associatedLayoutObjectOf() to handle ::first-letter pseudo-element correctly

third_party/WebKit/Source/core/editing/VisibleUnits.cpp

Index: third_party/WebKit/Source/core/editing/VisibleUnits.cpp
diff --git a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
index 358c9b1ae37eaa29b6eab16bc94b8caa69b7b1c1..1dc372711f28c0413df1308baea10b38d3362fcd 100644
--- a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
+++ b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
@@ -2171,28 +2171,40 @@ VisiblePosition visiblePositionForContentsPoint(const IntPoint& contentsPoint, L
 
 // TODO(yosin): We should use |associatedLayoutObjectOf()| in "VisibleUnits.cpp"
 // where it takes |LayoutObject| from |Position|.
-static LayoutObject* associatedLayoutObjectOf(const Node& node, int offsetInNode)
+LayoutObject* associatedLayoutObjectOf(const Node& node, int offsetInNode)
 {
     ASSERT(offsetInNode >= 0);
     LayoutObject* layoutObject = node.layoutObject();
     if (!node.isTextNode() || !layoutObject || !toLayoutText(layoutObject)->isTextFragment())
         return layoutObject;
+    // ::first-letter pseudo element yields following layout objects.
+    // |Text::layoutObject()| returns |LayoutTextFragment| for first-letter
+    // patter, e.g. "B\n", or remaining part "abc".

[tkent, 2016/01/29 03:52:16]

patter -> part?

I don't understand what you mean by "e.g. "B\n", or remaining part "abc"."

[yosin_UTC9, 2016/01/29 05:27:45]

Add more explanation about first-letter.

+    // Note: Remaining part can be empty if all characters in first-letter, e.g.
+    // "(a)".
+    //  LayoutBlockFlow {DIV} at (0,0) size 784x55
+    //    LayoutInline {<pseudo:first-letter>} at (0,0) size 22x53
+    //      LayoutTextFragment (anonymous) at (0,1) size 22x53
+    //        text run at (0,1) width 22: "a"
+    //    LayoutTextFragment {#text} at (21,30) size 16x17
+    //      text run at (21,30) width 16: "bc"
     LayoutTextFragment* layoutTextFragment = toLayoutTextFragment(layoutObject);
-    if (layoutTextFragment->isRemainingTextLayoutObject()) {
-        if (static_cast<unsigned>(offsetInNode) >= layoutTextFragment->start())
-            return layoutObject;
-        LayoutObject* firstLetterLayoutObject = layoutTextFragment->firstLetterPseudoElement()->layoutObject();
-        if (!firstLetterLayoutObject)
-            return nullptr;
-        // TODO(yosin): We're not sure when |firstLetterLayoutObject| has
-        // multiple child layout object.
-        ASSERT(firstLetterLayoutObject->slowFirstChild() == firstLetterLayoutObject->slowLastChild());
-        return firstLetterLayoutObject->slowFirstChild();
-    }
-    // TODO(yosin): We should rename |LayoutTextFramge::length()| instead of
-    // |end()|, once |LayoutTextFramge| has it. See http://crbug.com/545789
-    ASSERT(static_cast<unsigned>(offsetInNode) <= layoutTextFragment->start() + layoutTextFragment->fragmentLength());
-    return layoutTextFragment;
+    if (!layoutTextFragment->isRemainingTextLayoutObject()) {
+        // In case of there are no visible characters after first letter, e.g.
+        // "B\n"
+        ASSERT(static_cast<unsigned>(offsetInNode) <= layoutTextFragment->start() + layoutTextFragment->fragmentLength());
+        return layoutTextFragment;
+    }
+    // In case of |node| contains first-letter only, e.g. <div>"a" "bc"</div>
+    // we have "a" is associated to |LayoutTextFragment| with
+    // |isRemainingTextLayoutObject()| == true and |fragmentLength()| == 0.
+    if (layoutTextFragment->fragmentLength() && static_cast<unsigned>(offsetInNode) >= layoutTextFragment->start())
+        return layoutObject;
+    LayoutObject* firstLetterLayoutObject = layoutTextFragment->firstLetterPseudoElement()->layoutObject();
+    // TODO(yosin): We're not sure when |firstLetterLayoutObject| has
+    // multiple child layout object.
+    ASSERT(firstLetterLayoutObject->slowFirstChild() == firstLetterLayoutObject->slowLastChild());
+    return firstLetterLayoutObject->slowFirstChild();
 }
 
 int caretMinOffset(const Node* node)