Move default style for <dialog> to html.css

This is a follow-up of Blink r181385.

BUG=402536

Review URL: https://codereview.chromium.org/553353002

git-svn-id: svn://svn.chromium.org/blink/trunk@181710 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/css/html.css

@@ -1057,6 +1057,32 @@ textarea[dir=auto i] {
     unicode-bidi: -webkit-plaintext;
 }
 
+dialog:not([open]) {
+    display: none
+}
+
+dialog {
+    position: absolute;
+    left: 0;
+    right: 0;
+    width: -webkit-fit-content;
+    height: -webkit-fit-content;
+    margin: auto;
+    border: solid;
+    padding: 1em;
+    background: white;
+    color: black
+}
+
+dialog::backdrop {
+    position: fixed;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    background: rgba(0,0,0,0.1)
+}
+
 /* page */
 
 @page {

third_party/WebKit/Source/core/rendering/RenderTheme.cpp

@@ -406,14 +406,8 @@ bool RenderTheme::paintDecorations(RenderObject* o, const PaintInfo& paintInfo,
 String RenderTheme::extraDefaultStyleSheet()
 {
     StringBuilder runtimeCSS;
-    runtimeCSS.appendLiteral("dialog:not([open]) { display: none; }");
-    runtimeCSS.appendLiteral("dialog { position: absolute; left: 0; right: 0; width: -webkit-fit-content; height: -webkit-fit-content; margin: auto; border: solid; padding: 1em; background: white; color: black;}");
-    runtimeCSS.appendLiteral("dialog::backdrop { position: fixed; top: 0; right: 0; bottom: 0; left: 0; background: rgba(0,0,0,0.1); }");
-
-    if (RuntimeEnabledFeatures::contextMenuEnabled()) {
+    if (RuntimeEnabledFeatures::contextMenuEnabled())
         runtimeCSS.appendLiteral("menu[type=\"popup\" i] { display: none; }");
-    }
-
     return runtimeCSS.toString();
 }