[DevTools] Support async step in from arbitrary position

third_party/WebKit/Source/devtools/front_end/text_editor/cmdevtools.css

 .CodeMirror {
     line-height: 1.2em !important;
     background-color: transparent !important;
     color: #222;
 }
 
 .CodeMirror-linewidget {
     overflow: visible !important;
 }
 
@@ skipping 46 matching lines @@
     margin-left: -1px;
 }
 
 .CodeMirror .source-frame-continue-to-location-end {
     border-right-width: 1px;
     margin-right: -1px;
 }
 
 .CodeMirror .source-frame-async-step-in {
     outline: 0;
-    background-color: hsl(100, 46%, 77%);
+    background-color: hsla(100, 46%, 80%, 1);
     cursor: pointer;
-}
-
-.CodeMirror :not(.source-frame-async-step-in) + .source-frame-async-step-in:before {
-    -webkit-user-select: none;
-    background-image: -webkit-image-set(url(Images/smallIcons.png) 1x, url(Images/smallIcons_2x.png) 2x);
-    background-position: 1px 51px;
-    content: "aa";
-    color: transparent;
-    text-shadow: none;
-    height: 10px;
-    width: 10px;
+    border: 1px solid transparent;
+    border-left-width: 0;
+    border-right-width: 0;
 }
 
 .source-frame-async-step-in-hovered .source-frame-async-step-in {
-    background-color: hsl(100, 79%, 77%);
+    background-color: hsl(96, 53%, 65%);
+    border-color: rgb(100, 154, 100);
+}
+
+.source-frame-async-step-in-hovered .source-frame-async-step-in-start {
+    border-left-width: 1px;
+    margin-left: -1px;
+}
+
+.source-frame-async-step-in-hovered .source-frame-async-step-in-end {
+    border-right-width: 1px;
+    margin-right: -1px;
 }
 
 .CodeMirror-readonly .CodeMirror-cursor {
     display: none;
 }
 
 .CodeMirror .CodeMirror-gutters {
     border-right: 1px solid rgb(187, 187, 187);
     background-color: #eee;
 }
@@ skipping 384 matching lines @@
 
 .CodeMirror .auto-complete-text {
     color: rgb(128,128,128);
 }
 
 /** Prevent the codemirror textarea from stealing PageUp events **/
 .CodeMirror textarea {
     resize: none;
     overflow: hidden;
 }