Bug 1575650 - Fix initial megabar size in new windows. r=harry

Differential Revision: https://phabricator.services.mozilla.com/D43280

--HG--
extra : moz-landing-system : lando

browser/components/urlbar/UrlbarInput.jsm

@@ -884,6 +884,7 @@ class UrlbarInput {
     );
     this._layoutBreakoutPlaceholder.style.height = px(inputRect.height);
     this.textbox.before(this._layoutBreakoutPlaceholder);
+    this.setAttribute("breakout", "true");
   }
 
   endLayoutBreakout(force) {
@@ -894,6 +895,7 @@ class UrlbarInput {
     ) {
       return;
     }
+    this.removeAttribute("breakout");
     if (this._layoutBreakoutPlaceholder) {
       this._layoutBreakoutPlaceholder.remove();
       this._layoutBreakoutPlaceholder = null;

browser/themes/shared/urlbar-searchbar.inc.css

@@ -84,8 +84,7 @@
   border-color: var(--toolbar-field-focus-border-color);
 }
 
-#urlbar.megabar:not(.hidden-focus)[focused="true"],
-#urlbar.megabar[open="true"] {
+#urlbar[breakout] {
   position: absolute;
   z-index: 2;
   top: 0;
@@ -96,12 +95,11 @@
   padding: calc(3px + @urlbarBreakoutExtend@) 0;
 }
 
-#urlbar.megabar[open="true"] {
-  padding-bottom: 0 !important;
+#urlbar[breakout][open="true"] {
+  padding-bottom: 0;
 }
 
-#urlbar.megabar:not(.hidden-focus)[focused="true"] > #urlbar-input-container,
-#urlbar.megabar[open="true"] > #urlbar-input-container {
+#urlbar[breakout] > #urlbar-input-container {
   width: 100%;
 }