Enable RegionBasedColumns runtime flag for stable.

LayoutTests/platform/mac/virtual/stable/fast/multicol/max-height-columns-block-expected.txt

Index: LayoutTests/platform/mac/virtual/stable/fast/multicol/max-height-columns-block-expected.txt
diff --git a/LayoutTests/platform/mac/virtual/stable/fast/multicol/max-height-columns-block-expected.txt b/LayoutTests/platform/mac/virtual/stable/fast/multicol/max-height-columns-block-expected.txt
deleted file mode 100644
index 466de0d31edd13ba758d9a036a542b45e56101ec..0000000000000000000000000000000000000000
--- a/LayoutTests/platform/mac/virtual/stable/fast/multicol/max-height-columns-block-expected.txt
+++ /dev/null
@@ -1,47 +0,0 @@
-layer at (0,0) size 800x600
-  LayoutView at (0,0) size 800x600
-layer at (0,0) size 800x600
-  LayoutBlockFlow {HTML} at (0,0) size 800x600
-    LayoutBlockFlow {BODY} at (8,8) size 784x584
-      LayoutBlockFlow (anonymous) at (0,0) size 784x72
-        LayoutText {#text} at (0,0) size 784x72
-          text run at (0,0) width 439: "This is capturing current behavior, but it's not clear that it is correct. "
-          text run at (438,0) width 299: "It's not clear if max-height on a columns block"
-          text run at (0,18) width 299: "constitutes a constraint on the columns or not. "
-          text run at (298,18) width 486: "You obviously begin trying to balance, but only run into the constraint once"
-          text run at (0,36) width 296: "the balanced columns exceed the max-height. "
-          text run at (295,36) width 334: "It's not clear that you should suddenly shift to a fill. "
-          text run at (628,36) width 136: "Our current behavior"
-          text run at (0,54) width 524: "(which matches Firefox) is to just overflow without changing from balance to fill."
-layer at (8,80) size 404x64
-  LayoutBlockFlow {DIV} at (0,72) size 404x64 [border: (2px solid #000000)]
-    LayoutText {#text} at (2,2) size 51x112
-      text run at (2,2) width 43: "This"
-      text run at (2,30) width 17: "is"
-      text run at (2,58) width 51: "some"
-      text run at (2,86) width 36: "text"
-    LayoutBR {BR} at (37,108) size 1x0
-    LayoutText {#text} at (2,114) size 51x112
-      text run at (2,114) width 43: "This"
-      text run at (2,142) width 17: "is"
-      text run at (2,170) width 51: "some"
-      text run at (2,198) width 36: "text"
-    LayoutBR {BR} at (37,220) size 1x0
-    LayoutText {#text} at (2,226) size 51x112
-      text run at (2,226) width 43: "This"
-      text run at (2,254) width 17: "is"
-      text run at (2,282) width 51: "some"
-      text run at (2,310) width 36: "text"
-    LayoutBR {BR} at (37,332) size 1x0
-    LayoutText {#text} at (2,338) size 51x112
-      text run at (2,338) width 43: "This"
-      text run at (2,366) width 17: "is"
-      text run at (2,394) width 51: "some"
-      text run at (2,422) width 36: "text"
-    LayoutBR {BR} at (37,444) size 1x0
-    LayoutText {#text} at (2,450) size 51x112
-      text run at (2,450) width 43: "This"
-      text run at (2,478) width 17: "is"
-      text run at (2,506) width 51: "some"
-      text run at (2,534) width 36: "text"
-    LayoutBR {BR} at (37,556) size 1x0