[DevTools] Add groups to device select.

Source/devtools/front_end/responsiveDesignView.css

Index: Source/devtools/front_end/responsiveDesignView.css
diff --git a/Source/devtools/front_end/responsiveDesignView.css b/Source/devtools/front_end/responsiveDesignView.css
index 5c8948496db2ef1da0f96f0c5bcece7121a3b203..fdeb30274e6b4982f67d6419e2846f010caa13b0 100644
--- a/Source/devtools/front_end/responsiveDesignView.css
+++ b/Source/devtools/front_end/responsiveDesignView.css
@@ -115,7 +115,7 @@
     flex-direction: row;
     align-items: center;
     justify-content: space-between;
-    height: 22px;
+    height: 23px;
     overflow: hidden;
 }
 
@@ -142,8 +142,7 @@
     text-align: left;
     background-color: transparent;
     border: none;
-    margin: 0;
-    margin-bottom: 4px;
+    margin: 0 1px 1px 0;
     padding: 3px 2px;
 }
 
@@ -292,7 +291,7 @@ body.platform-mac .responsive-design-toolbar select {
 }
 
 .responsive-design-section-device select {
-    width: 220px;
+    width: 180px;
 }
 
 .responsive-design-section-device input[type='text'],
@@ -344,4 +343,9 @@ body.platform-mac .responsive-design-toolbar select {
 .responsive-design-warning > span {
     flex: auto;
     padding-left: 3px;
+    overflow: hidden;
 }
+
+.responsive-design-warning > div {
+    flex: none;
+}