Move and rename RenderBR to LayoutBR.

LayoutTests/platform/mac/fast/forms/basic-inputs-expected.txt

 layer at (0,0) size 800x600
   RenderView at (0,0) size 800x600
 layer at (0,0) size 800x600
   RenderBlock {HTML} at (0,0) size 800x600
     RenderBody {BODY} at (8,8) size 470x582
       RenderBlock (anonymous) at (0,0) size 470x306
         RenderText {#text} at (0,0) size 332x18
           text run at (0,0) width 332: "This tests basic inputs. Here's what you should see: "
-        RenderBR {BR} at (331,14) size 1x0
-        RenderBR {BR} at (0,18) size 0x18
+        LayoutBR {BR} at (331,14) size 1x0
+        LayoutBR {BR} at (0,18) size 0x18
         RenderText {#text} at (0,36) size 462x54
           text run at (0,36) width 445: "first line: the letter \"a\" and then a text input field filled with repeating"
           text run at (0,54) width 86: "\"foobarbaz\", "
           text run at (85,54) width 377: "then the word \"text\" followed by a disabled text input field"
           text run at (0,72) width 336: "filled with \"foo\" and then the letter \"b\" and then \"a\" "
-        RenderBR {BR} at (335,86) size 1x0
-        RenderBR {BR} at (0,90) size 0x18
+        LayoutBR {BR} at (335,86) size 1x0
+        LayoutBR {BR} at (0,90) size 0x18
         RenderText {#text} at (0,108) size 469x54
           text run at (0,108) width 439: "second line: and then a password input field that's filled and then the"
           text run at (0,126) width 469: "word \"password\" and then a disabled password field that's filled and then"
           text run at (0,144) width 86: "the letter \"b\" "
-        RenderBR {BR} at (85,158) size 1x0
-        RenderBR {BR} at (0,162) size 0x18
+        LayoutBR {BR} at (85,158) size 1x0
+        LayoutBR {BR} at (0,162) size 0x18
         RenderText {#text} at (0,180) size 459x36
           text run at (0,180) width 459: "third line: the letter \"a\" and then a checkbox (unchecked) with the word"
           text run at (0,198) width 360: "\"checkbox\" and then a disabled checkbox and letter \"b\" "
-        RenderBR {BR} at (359,212) size 1x0
-        RenderBR {BR} at (0,216) size 0x18
+        LayoutBR {BR} at (359,212) size 1x0
+        LayoutBR {BR} at (0,216) size 0x18
         RenderText {#text} at (0,234) size 457x54
           text run at (0,234) width 411: "fourth line: the last line has the letter \"a\" and then a redio button"
           text run at (0,252) width 457: "(unselected) and then the word \"radio\" and then a disabled radio button"
           text run at (0,270) width 113: "and the letter \"b\" "
-        RenderBR {BR} at (112,284) size 1x0
-        RenderBR {BR} at (0,288) size 0x18
+        LayoutBR {BR} at (112,284) size 1x0
+        LayoutBR {BR} at (0,288) size 0x18
       RenderBlock {DIV} at (10,316) size 450x40 [border: (1px solid #FF0000)]
         RenderText {#text} at (1,1) size 8x18
           text run at (1,1) width 8: "a"
         LayoutTextControl {INPUT} at (8.09,1) size 123x19 [bgcolor=#FFFFFF] [border: (2px inset #EEEEEE)]
         RenderText {#text} at (131,1) size 29x18
           text run at (131,1) width 29: "text "
         LayoutTextControl {INPUT} at (159.09,1) size 123x19 [color=#545454] [bgcolor=#FFFFFF] [border: (2px inset #EEEEEE)]
         RenderText {#text} at (282,1) size 20x18
           text run at (282,1) width 13: "b "
           text run at (294,1) width 8: "a"
@@ skipping 30 matching lines @@
     RenderText {#text} at (0,0) size 18x13
       text run at (0,0) width 18: "foo"
 layer at (322,328) size 117x13
   RenderBlock {DIV} at (3,3) size 117x13
     RenderText {#text} at (0,0) size 19x13
       text run at (0,0) width 19: "\x{2022}\x{2022}\x{2022}"
 layer at (86,347) size 117x13
   RenderBlock {DIV} at (3,3) size 117x13
     RenderText {#text} at (0,0) size 19x13
       text run at (0,0) width 19: "\x{2022}\x{2022}\x{2022}"