Row with only spanning cells have a height of 0.

LayoutTests/platform/win/tables/mozilla/core/row_span-expected.txt

Index: LayoutTests/platform/win/tables/mozilla/core/row_span-expected.txt
diff --git a/LayoutTests/platform/win/tables/mozilla/core/row_span-expected.txt b/LayoutTests/platform/win/tables/mozilla/core/row_span-expected.txt
index eec76a2d0d78d88672d5e4c60b86d316a8629238..4d7ab326d4782d8888e5d56fa536de52e3de2704 100644
--- a/LayoutTests/platform/win/tables/mozilla/core/row_span-expected.txt
+++ b/LayoutTests/platform/win/tables/mozilla/core/row_span-expected.txt
@@ -1,8 +1,8 @@
-layer at (0,0) size 785x882
+layer at (0,0) size 785x904
   RenderView at (0,0) size 785x600
-layer at (0,0) size 785x882
-  RenderBlock {HTML} at (0,0) size 785x882
-    RenderBody {BODY} at (8,8) size 769x866
+layer at (0,0) size 785x904
+  RenderBlock {HTML} at (0,0) size 785x904
+    RenderBody {BODY} at (8,8) size 769x888
       RenderBlock (anonymous) at (0,0) size 769x20
         RenderText {#text} at (0,0) size 87x19
           text run at (0,0) width 87: "ROWSPANS"
@@ -129,19 +129,19 @@ layer at (0,0) size 785x882
             RenderTableCell {TD} at (2,28) size 55x24 [border: (1px inset #808080)] [r=1 c=0 rs=1 cs=2]
               RenderText {#text} at (12,2) size 31x19
                 text run at (12,2) width 31: "three"
-      RenderTable {TABLE} at (0,474) size 56x8 [border: (1px outset #808080)]
-        RenderTableSection {TBODY} at (1,1) size 54x6
+      RenderTable {TABLE} at (0,474) size 56x30 [border: (1px outset #808080)]
+        RenderTableSection {TBODY} at (1,1) size 54x28
           RenderTableRow {TR} at (0,2) size 54x0
-            RenderTableCell {TD} at (2,-9) size 24x24 [border: (1px inset #808080)] [r=0 c=0 rs=2 cs=1]
+            RenderTableCell {TD} at (2,2) size 24x24 [border: (1px inset #808080)] [r=0 c=0 rs=2 cs=1]
               RenderText {#text} at (2,2) size 20x19
                 text run at (2,2) width 20: "foo"
-          RenderTableRow {TR} at (0,4) size 54x0
-            RenderTableCell {TD} at (28,-8) size 24x24 [border: (1px inset #808080)] [r=1 c=1 rs=2 cs=1]
+          RenderTableRow {TR} at (0,4) size 54x22
+            RenderTableCell {TD} at (28,3) size 24x24 [border: (1px inset #808080)] [r=1 c=1 rs=2 cs=1]
               RenderText {#text} at (2,2) size 20x19
                 text run at (2,2) width 20: "bar"
-      RenderBlock (anonymous) at (0,482) size 769x20
+      RenderBlock (anonymous) at (0,504) size 769x20
         RenderBR {BR} at (0,0) size 0x19
-      RenderTable {TABLE} at (0,502) size 602x364 [border: (1px outset #808080)]
+      RenderTable {TABLE} at (0,524) size 602x364 [border: (1px outset #808080)]
         RenderTableSection {TBODY} at (1,1) size 600x362
           RenderTableRow {TR} at (0,0) size 600x0
             RenderTableCell {TD} at (0,0) size 512x362 [bgcolor=#FFFFFF] [border: (1px inset #808080)] [r=0 c=0 rs=2 cs=2]