Fix for bug 86532. outliner doesn't display large fonts properly.

- added |min-height: 18px| to |-moz-tree-row| pseudoelement
- changed height to |height: 1.3em|
- the final height is aligned to even number.
- GetRowHeight() moved to Init()

r=bryner, sr=hyatt, a=asa

suite/themes/modern/global/tree.css

@@ -58,7 +58,8 @@ tree {
 
 treechildren:-moz-tree-row {
   border: 1px solid transparent;
-  height: 18px;
+  min-height: 18px;
+  height: 1.3em;
 }
 
 treechildren:-moz-tree-row(selected) {