Correct multicol-rule-fraction-3-ref.xht offsets.

I'm not sure what this test really provides. The name suggests that it
has something to do with column rules, but there are no column rules
defined. There is something that looks like rules, but they are in fact
absolutely positioned boxes placed in the middle of the column gaps.
Anyway, let's at least use the same offsets in the test and in the ref,
instead of being slightly off.

Bug: 788337
Change-Id: Ic6a07e7020d54e545413c1c7a68f5acdd52019a4
Reviewed-on: https://chromium-review.googlesource.com/810966Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522096}

third_party/WebKit/LayoutTests/TestExpectations

@@ -2408,7 +2408,6 @@ crbug.com/788337 external/wpt/css/css-multicol/multicol-count-computed-003.xht [
 crbug.com/788337 external/wpt/css/css-multicol/multicol-count-computed-005.xht [ Failure ]
 crbug.com/788337 external/wpt/css/css-multicol/multicol-height-block-child-001.xht [ Failure ]
 crbug.com/788337 external/wpt/css/css-multicol/multicol-rule-004.xht [ Failure ]
-crbug.com/788337 external/wpt/css/css-multicol/multicol-rule-fraction-003.xht [ Failure ]
 crbug.com/788337 external/wpt/css/css-multicol/multicol-rule-inset-000.xht [ Failure ]
 crbug.com/788337 external/wpt/css/css-multicol/multicol-rule-outset-000.xht [ Failure ]
 crbug.com/788337 external/wpt/css/css-multicol/multicol-rule-style-inset-001.xht [ Failure ]

third_party/WebKit/LayoutTests/external/wpt/css/css-multicol/multicol-rule-fraction-3-ref.xht

@@ -32,9 +32,9 @@ div div {
 	background: blue;
 	width: 1em;
 }
-#a1 {left: 2.43em;}
+#a1 {left: 2.4em;}
 #a2 {left: 3.75em;}
-#a3 {left: 6.13em;}
+#a3 {left: 6.15em;}
 #a4 {left: 7.5em;}
 #a5 {left: 9.9em;}
 #a6 {left: 11.25em;}