Use border-box sizing for the HR element.

LayoutTests/platform/linux/tables/mozilla_expected_failures/core/col_span2-expected.txt

Index: LayoutTests/platform/linux/tables/mozilla_expected_failures/core/col_span2-expected.txt
diff --git a/LayoutTests/platform/linux/tables/mozilla_expected_failures/core/col_span2-expected.txt b/LayoutTests/platform/linux/tables/mozilla_expected_failures/core/col_span2-expected.txt
index ab3dae629bf39496f7cad5c2413c629f7308ca26..8b930aaab5466384248cbd91549a41fe57b0c84b 100644
--- a/LayoutTests/platform/linux/tables/mozilla_expected_failures/core/col_span2-expected.txt
+++ b/LayoutTests/platform/linux/tables/mozilla_expected_failures/core/col_span2-expected.txt
@@ -235,7 +235,7 @@ layer at (0,0) size 785x5885 backgroundClip at (0,0) size 785x600 clip at (0,0)
                 text run at (2,2) width 21: "zap"
       LayoutBlockFlow (anonymous) at (0,834) size 769x20
         LayoutBR {BR} at (0,0) size 0x19
-      LayoutBlockFlow {HR} at (0,862) size 202x2 [border: (1px inset #EEEEEE)]
+      LayoutBlockFlow {HR} at (0,862) size 200x2 [border: (1px inset #EEEEEE)]
       LayoutTable {TABLE} at (0,872) size 210x56 [border: (1px outset #808080)]
         LayoutTableSection {TBODY} at (1,1) size 208x54
           LayoutTableRow {TR} at (0,2) size 208x24
@@ -254,7 +254,7 @@ layer at (0,0) size 785x5885 backgroundClip at (0,0) size 785x600 clip at (0,0)
                 text run at (2,2) width 52: "200CS3"
       LayoutBlockFlow (anonymous) at (0,928) size 769x20
         LayoutBR {BR} at (0,0) size 0x19
-      LayoutBlockFlow {HR} at (0,956) size 202x2 [border: (1px inset #EEEEEE)]
+      LayoutBlockFlow {HR} at (0,956) size 200x2 [border: (1px inset #EEEEEE)]
       LayoutTable {TABLE} at (0,966) size 210x56 [border: (1px outset #808080)]
         LayoutTableSection {TBODY} at (1,1) size 208x54
           LayoutTableRow {TR} at (0,2) size 208x24
@@ -328,7 +328,7 @@ layer at (0,0) size 785x5885 backgroundClip at (0,0) size 785x600 clip at (0,0)
         LayoutText {#text} at (0,0) size 278x19
           text run at (0,0) width 278: "fixed table - spanned cols based on fix widths "
         LayoutBR {BR} at (278,15) size 0x0
-      LayoutBlockFlow {HR} at (0,1358) size 402x2 [border: (1px inset #EEEEEE)]
+      LayoutBlockFlow {HR} at (0,1358) size 400x2 [border: (1px inset #EEEEEE)]
       LayoutTable {TABLE} at (0,1368) size 534x65 [bgcolor=#FFA500] [border: (1px outset #808080)]
         LayoutTableSection {TBODY} at (1,1) size 532x63
           LayoutTableRow {TR} at (0,5) size 532x24
@@ -939,7 +939,7 @@ layer at (0,0) size 785x5885 backgroundClip at (0,0) size 785x600 clip at (0,0)
       LayoutBlockFlow (anonymous) at (0,4050) size 769x40
         LayoutBR {BR} at (0,0) size 0x19
         LayoutBR {BR} at (0,20) size 0x19
-      LayoutBlockFlow {HR} at (0,4098) size 602x2 [border: (1px inset #EEEEEE)]
+      LayoutBlockFlow {HR} at (0,4098) size 600x2 [border: (1px inset #EEEEEE)]
       LayoutTable {TABLE} at (0,4108) size 645x145 [border: (1px outset #808080)]
         LayoutTableSection {TBODY} at (1,1) size 643x143
           LayoutTableRow {TR} at (0,5) size 643x104