Row with only spanning cells have a height of 0.

LayoutTests/platform/win/tables/mozilla/bugs/bug6304-expected.txt

Index: LayoutTests/platform/win/tables/mozilla/bugs/bug6304-expected.txt
diff --git a/LayoutTests/platform/win/tables/mozilla/bugs/bug6304-expected.txt b/LayoutTests/platform/win/tables/mozilla/bugs/bug6304-expected.txt
index e19da557b0cd54e10dff52eff4f7567a1eff16b0..218f7187113f27568fa4b071c444528b7b0d214e 100644
--- a/LayoutTests/platform/win/tables/mozilla/bugs/bug6304-expected.txt
+++ b/LayoutTests/platform/win/tables/mozilla/bugs/bug6304-expected.txt
@@ -163,13 +163,13 @@ layer at (0,0) size 800x600
                       RenderTableCell {TD} at (59,93) size 22x22 [border: (1px inset #808080)] [r=4 c=2 rs=1 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "5,3"
-              RenderTableCell {TD} at (308,2) size 73x152 [border: (1px inset #808080)] [r=0 c=3 rs=1 cs=1]
-                RenderTable {TABLE} at (6,6) size 61x140 [bgcolor=#FFFFFF] [border: (1px outset #808080)]
+              RenderTableCell {TD} at (308,2) size 73x163 [border: (1px inset #808080)] [r=0 c=3 rs=1 cs=1]
+                RenderTable {TABLE} at (6,6) size 61x151 [bgcolor=#FFFFFF] [border: (1px outset #808080)]
                   RenderBlock {CAPTION} at (0,0) size 61x20
                     RenderInline {NOBR} at (0,0) size 55x19
                       RenderText {#text} at (3,0) size 55x19
                         text run at (3,0) width 55: "Table IV"
-                  RenderTableSection {TBODY} at (1,21) size 59x118
+                  RenderTableSection {TBODY} at (1,21) size 59x129
                     RenderTableRow {TR} at (0,5) size 59x22
                       RenderTableCell {TD} at (5,5) size 22x22 [border: (1px inset #808080)] [r=0 c=0 rs=1 cs=1]
                         RenderText {#text} at (1,1) size 20x19
@@ -181,22 +181,22 @@ layer at (0,0) size 800x600
                       RenderTableCell {TD} at (5,32) size 22x22 [border: (1px inset #808080)] [r=1 c=0 rs=1 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "2,1"
-                      RenderTableCell {TD} at (32,34) size 22x22 [border: (1px inset #808080)] [r=1 c=1 rs=2 cs=1]
+                      RenderTableCell {TD} at (32,40) size 22x22 [border: (1px inset #808080)] [r=1 c=1 rs=2 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "2,2"
-                    RenderTableRow {TR} at (0,59) size 59x0
-                      RenderTableCell {TD} at (5,61) size 22x22 [border: (1px inset #808080)] [r=2 c=0 rs=2 cs=1]
+                    RenderTableRow {TR} at (0,59) size 59x11
+                      RenderTableCell {TD} at (5,67) size 22x22 [border: (1px inset #808080)] [r=2 c=0 rs=2 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "3,1"
-                    RenderTableRow {TR} at (0,64) size 59x22
-                      RenderTableCell {TD} at (32,64) size 22x22 [border: (1px inset #808080)] [r=3 c=1 rs=1 cs=1]
+                    RenderTableRow {TR} at (0,75) size 59x22
+                      RenderTableCell {TD} at (32,75) size 22x22 [border: (1px inset #808080)] [r=3 c=1 rs=1 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "4,2"
-                    RenderTableRow {TR} at (0,91) size 59x22
-                      RenderTableCell {TD} at (5,91) size 22x22 [border: (1px inset #808080)] [r=4 c=0 rs=1 cs=1]
+                    RenderTableRow {TR} at (0,102) size 59x22
+                      RenderTableCell {TD} at (5,102) size 22x22 [border: (1px inset #808080)] [r=4 c=0 rs=1 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "5,1"
-                      RenderTableCell {TD} at (32,91) size 22x22 [border: (1px inset #808080)] [r=4 c=1 rs=1 cs=1]
+                      RenderTableCell {TD} at (32,102) size 22x22 [border: (1px inset #808080)] [r=4 c=1 rs=1 cs=1]
                         RenderText {#text} at (1,1) size 20x19
                           text run at (1,1) width 20: "5,2"
       RenderBlock {HR} at (0,224) size 784x2 [border: (1px inset #EEEEEE)]