Move and rename RenderBR to LayoutBR.

LayoutTests/platform/mac/editing/input/reveal-caret-of-multiline-contenteditable-expected.txt

 layer at (0,0) size 800x600
   RenderView at (0,0) size 800x600
 layer at (0,0) size 800x216
   RenderBlock {HTML} at (0,0) size 800x216
     RenderBody {BODY} at (8,8) size 784x200
       RenderBlock {DIV} at (0,0) size 784x18
         RenderText {#text} at (0,0) size 610x18
           text run at (0,0) width 610: "When the caret is scrolled out, on starting typing it must be brought to the center of the control."
 layer at (8,26) size 784x182 clip at (9,27) size 767x165 scrollY 251.00 scrollHeight 558
   RenderBlock {DIV} at (0,18) size 784x182 [border: (1px solid #000000)]
     RenderText {#text} at (1,1) size 16x18
       text run at (1,1) width 16: "00"
-    RenderBR {BR} at (17,1) size 0x18
+    LayoutBR {BR} at (17,1) size 0x18
     RenderText {#text} at (1,19) size 16x18
       text run at (1,19) width 16: "01"
-    RenderBR {BR} at (17,19) size 0x18
+    LayoutBR {BR} at (17,19) size 0x18
     RenderText {#text} at (1,37) size 16x18
       text run at (1,37) width 16: "02"
-    RenderBR {BR} at (17,37) size 0x18
+    LayoutBR {BR} at (17,37) size 0x18
     RenderText {#text} at (1,55) size 16x18
       text run at (1,55) width 16: "03"
-    RenderBR {BR} at (17,55) size 0x18
+    LayoutBR {BR} at (17,55) size 0x18
     RenderText {#text} at (1,73) size 16x18
       text run at (1,73) width 16: "04"
-    RenderBR {BR} at (17,73) size 0x18
+    LayoutBR {BR} at (17,73) size 0x18
     RenderText {#text} at (1,91) size 16x18
       text run at (1,91) width 16: "05"
-    RenderBR {BR} at (17,91) size 0x18
+    LayoutBR {BR} at (17,91) size 0x18
     RenderText {#text} at (1,109) size 16x18
       text run at (1,109) width 16: "06"
-    RenderBR {BR} at (17,109) size 0x18
+    LayoutBR {BR} at (17,109) size 0x18
     RenderText {#text} at (1,127) size 16x18
       text run at (1,127) width 16: "07"
-    RenderBR {BR} at (17,127) size 0x18
+    LayoutBR {BR} at (17,127) size 0x18
     RenderText {#text} at (1,145) size 16x18
       text run at (1,145) width 16: "08"
-    RenderBR {BR} at (17,145) size 0x18
+    LayoutBR {BR} at (17,145) size 0x18
     RenderText {#text} at (1,163) size 16x18
       text run at (1,163) width 16: "09"
-    RenderBR {BR} at (17,163) size 0x18
+    LayoutBR {BR} at (17,163) size 0x18
     RenderText {#text} at (1,181) size 16x18
       text run at (1,181) width 16: "10"
-    RenderBR {BR} at (17,181) size 0x18
+    LayoutBR {BR} at (17,181) size 0x18
     RenderText {#text} at (1,199) size 16x18
       text run at (1,199) width 16: "11"
-    RenderBR {BR} at (17,199) size 0x18
+    LayoutBR {BR} at (17,199) size 0x18
     RenderText {#text} at (1,217) size 16x18
       text run at (1,217) width 16: "12"
-    RenderBR {BR} at (17,217) size 0x18
+    LayoutBR {BR} at (17,217) size 0x18
     RenderText {#text} at (1,235) size 16x18
       text run at (1,235) width 16: "13"
-    RenderBR {BR} at (17,235) size 0x18
+    LayoutBR {BR} at (17,235) size 0x18
     RenderText {#text} at (1,253) size 16x18
       text run at (1,253) width 16: "14"
-    RenderBR {BR} at (17,253) size 0x18
+    LayoutBR {BR} at (17,253) size 0x18
     RenderText {#text} at (1,271) size 16x18
       text run at (1,271) width 16: "15"
-    RenderBR {BR} at (17,271) size 0x18
+    LayoutBR {BR} at (17,271) size 0x18
     RenderText {#text} at (1,289) size 16x18
       text run at (1,289) width 16: "16"
-    RenderBR {BR} at (17,289) size 0x18
+    LayoutBR {BR} at (17,289) size 0x18
     RenderText {#text} at (1,307) size 16x18
       text run at (1,307) width 16: "17"
-    RenderBR {BR} at (17,307) size 0x18
+    LayoutBR {BR} at (17,307) size 0x18
     RenderText {#text} at (1,325) size 26x18
       text run at (1,325) width 26: ">18"
-    RenderBR {BR} at (26,325) size 1x18
+    LayoutBR {BR} at (26,325) size 1x18
     RenderText {#text} at (1,343) size 16x18
       text run at (1,343) width 16: "19"
-    RenderBR {BR} at (17,343) size 0x18
+    LayoutBR {BR} at (17,343) size 0x18
     RenderText {#text} at (1,361) size 16x18
       text run at (1,361) width 16: "20"
-    RenderBR {BR} at (17,361) size 0x18
+    LayoutBR {BR} at (17,361) size 0x18
     RenderText {#text} at (1,379) size 16x18
       text run at (1,379) width 16: "21"
-    RenderBR {BR} at (17,379) size 0x18
+    LayoutBR {BR} at (17,379) size 0x18
     RenderText {#text} at (1,397) size 16x18
       text run at (1,397) width 16: "22"
-    RenderBR {BR} at (17,397) size 0x18
+    LayoutBR {BR} at (17,397) size 0x18
     RenderText {#text} at (1,415) size 16x18
       text run at (1,415) width 16: "23"
-    RenderBR {BR} at (17,415) size 0x18
+    LayoutBR {BR} at (17,415) size 0x18
     RenderText {#text} at (1,433) size 16x18
       text run at (1,433) width 16: "24"
-    RenderBR {BR} at (17,433) size 0x18
+    LayoutBR {BR} at (17,433) size 0x18
     RenderText {#text} at (1,451) size 16x18
       text run at (1,451) width 16: "25"
-    RenderBR {BR} at (17,451) size 0x18
+    LayoutBR {BR} at (17,451) size 0x18
     RenderText {#text} at (1,469) size 16x18
       text run at (1,469) width 16: "26"
-    RenderBR {BR} at (17,469) size 0x18
+    LayoutBR {BR} at (17,469) size 0x18
     RenderText {#text} at (1,487) size 16x18
       text run at (1,487) width 16: "27"
-    RenderBR {BR} at (17,487) size 0x18
+    LayoutBR {BR} at (17,487) size 0x18
     RenderText {#text} at (1,505) size 16x18
       text run at (1,505) width 16: "28"
-    RenderBR {BR} at (17,505) size 0x18
+    LayoutBR {BR} at (17,505) size 0x18
     RenderText {#text} at (1,523) size 16x18
       text run at (1,523) width 16: "29"
-    RenderBR {BR} at (17,523) size 0x18
+    LayoutBR {BR} at (17,523) size 0x18
     RenderText {#text} at (1,541) size 16x18
       text run at (1,541) width 16: "30"
-    RenderBR {BR} at (17,541) size 0x18
+    LayoutBR {BR} at (17,541) size 0x18
 hidden layer at (8,26) size 8x18
   RenderBlock (positioned) {SPAN} at (8,26) size 8x18
     RenderText {#text} at (0,0) size 8x18
       text run at (0,0) width 8: "0"
 caret: position 1 of child 36 {#text} of child 5 {DIV} of body