Host Chrome OS GAIA signin page in webview

chrome/browser/resources/chromeos/login/screen_gaia_signin.css

Index: chrome/browser/resources/chromeos/login/screen_gaia_signin.css
diff --git a/chrome/browser/resources/chromeos/login/screen_gaia_signin.css b/chrome/browser/resources/chromeos/login/screen_gaia_signin.css
index 668470d3d9869c4586b2f04ff325dec87c9d7f74..37a28089cbaa946deedf1a611fad575c01d21675 100644
--- a/chrome/browser/resources/chromeos/login/screen_gaia_signin.css
+++ b/chrome/browser/resources/chromeos/login/screen_gaia_signin.css
@@ -89,6 +89,12 @@
   width: 400px;
 }
 
+webview#signin-frame {
+  display: block;
+  overflow: hidden;
+  padding: 0;
+}
+
 /* Simpler alignment if no right panel. */
 .no-right-panel #signin-frame {
   margin-left: 0;
@@ -121,6 +127,12 @@
   height: 100%;
 }
 
+#gaia-loading {
+  background-color: white;
+  height: 80%;
+  top: 80px;
+}
+
 #createSupervisedUserSeparator {
   background-color: rgba(128,128,128,0.3);
   height: 1px;