Separate VTTCue from VTTCueBox and LayoutVTTCue

Source/core/layout/LayoutVTTCue.h

Index: Source/core/layout/LayoutVTTCue.h
diff --git a/Source/core/layout/LayoutVTTCue.h b/Source/core/layout/LayoutVTTCue.h
index b3236d8aeb690a986926123ca179c482429c1459..e512d264f9816283afcb343f5def8bb548a5f1c2 100644
--- a/Source/core/layout/LayoutVTTCue.h
+++ b/Source/core/layout/LayoutVTTCue.h
@@ -31,12 +31,15 @@
 
 namespace blink {
 
-class VTTCue;
 class VTTCueBox;
 
 class LayoutVTTCue final : public LayoutBlockFlow {
 public:
-    explicit LayoutVTTCue(VTTCueBox*);
+    explicit LayoutVTTCue(ContainerNode*, float snapToLinesPosition);

[sof, 2015/07/20 08:15:39]

nit: can drop explicit now.

[philipj_slow, 2015/07/20 08:34:16]

Done, and also added explicit to the VTTCueBox constructor which now has just
one argument.

+
+    // The computed line position for snap-to-lines layout, and NaN for
+    // non-snap-to-lines layout where no adjustment should take place.
+    float snapToLinesPosition() { return m_snapToLinesPosition; }

[fs, 2015/07/17 14:31:48]

Any particular reason for not doing something like:

float snapToLinesPosition() const
{
    return toVTTCueBox(*node()).snapToLinesPosition();
}

?

Hmm, I guess we might not have a way to id a VTTCueBox, and adding one would
s*ck I suppose... Oh well.

(I really think that we shouldn't be recreating theses fragments at a whim...)

[philipj_slow, 2015/07/20 07:33:30]

Precisely, an isVTTCueBox would require an extra virtual on Node, and I didn't
think it was worth it, nor did static_cast<VTTCueBox*> seem appealing despite
currently being safe.

I was also tempted to use the style system to pass this float, by adding some
inline style that isn't actually used, but that seemed to clever. If passing
this extra information through the constructor turns out to be a problem (or
deemed ugly) either an explicit internal style property or an is/toVTTCueBox
would be OK.

 
 private:
     void layout() override;
@@ -44,9 +47,7 @@ private:
     void adjustForTopAndBottomMarginBorderAndPadding();
     void repositionCueSnapToLinesNotSet();
 
-    // VTTCue is kept alive by VTTCueBox.
-    GC_PLUGIN_IGNORE("http://crbug.com/509911")
-    VTTCue* m_cue;
+    float m_snapToLinesPosition;
 };
 
 } // namespace blink