Switch tracing to new flexbox.

tracing/tracing/ui/extras/chrome/cc/layer_view.css

Index: tracing/tracing/ui/extras/chrome/cc/layer_view.css
diff --git a/tracing/tracing/ui/extras/chrome/cc/layer_view.css b/tracing/tracing/ui/extras/chrome/cc/layer_view.css
index 612dbc2eb9a109fe2305fbd31942d5b39edd2f4d..c171beb9c51b7a757edf9f93ed96b460df1943f5 100644
--- a/tracing/tracing/ui/extras/chrome/cc/layer_view.css
+++ b/tracing/tracing/ui/extras/chrome/cc/layer_view.css
@@ -4,8 +4,8 @@
  */
 
 * /deep/ tr-ui-e-chrome-cc-layer-view {
-  -webkit-flex-direction: column;
-  display:  -webkit-flex;
+  flex-direction: column;
+  display:  flex;
   left: 0;
   position: relative;
   top: 0;
@@ -13,10 +13,10 @@
 
 * /deep/ tr-ui-e-chrome-cc-layer-view >
       tr-ui-e-chrome-cc-layer-tree-quad-stack-view {
-  -webkit-flex: 1 1 100%;
-  -webkit-flex-direction: column;
+  flex: 1 1 100%;
+  flex-direction: column;
   min-height: 0;
-  display: -webkit-flex;
+  display: flex;
   width: 100%;
 }