Fix getComputedStyle() for area element

The getComputedStyle() function didn't work as we expected for the area.
The reason is chrome set display area as none, this patch fix this problem.

This behavior matches Firefox.
The Internet Explorer 11 set area display as none.

BUG=392759

Review URL: https://codereview.chromium.org/442563002

git-svn-id: svn://svn.chromium.org/blink/trunk@180610 bbb929c8-8fbe-4397-9dbb-9b2b20218538
diff --git a/Source/core/css/html.css b/Source/core/css/html.css
index 91f074a..17f7402 100644
--- a/Source/core/css/html.css
+++ b/Source/core/css/html.css
@@ -650,7 +650,11 @@
     display: none
 }
 
-area, param {
+area {
+    display: inline
+}
+
+param {
     display: none
 }