Unprefix flexbox properties in various CSS files

Source/core/css/mediaControlsAndroid.css

Index: Source/core/css/mediaControlsAndroid.css
diff --git a/Source/core/css/mediaControlsAndroid.css b/Source/core/css/mediaControlsAndroid.css
index 184940203bc855eb69559e5f8c44e9566c58c5a1..0b111e0c78bc36ab65790715594fd576dc94a12b 100644
--- a/Source/core/css/mediaControlsAndroid.css
+++ b/Source/core/css/mediaControlsAndroid.css
@@ -37,12 +37,12 @@ audio::-webkit-media-controls-overlay-enclosure {
 }
 
 video::-webkit-media-controls-overlay-enclosure {
-    display: -webkit-flex;
+    display: flex;
     position: relative;
-    -webkit-flex-direction: column;
-    -webkit-justify-content: flex-end;
-    -webkit-align-items: center;
-    -webkit-flex: 1 1;
+    flex-direction: column;
+    justify-content: flex-end;
+    align-items: center;
+    flex: 1 1;
     width: 100%;
     max-width: 800px;
     text-indent: 0;
@@ -61,7 +61,7 @@ audio::-webkit-media-controls-mute-button, video::-webkit-media-controls-mute-bu
 
 video::-webkit-media-controls-overlay-play-button {
     -webkit-appearance: media-overlay-play-button;
-    display: -webkit-flex;
+    display: flex;
     position: absolute;
     top: 50%;
     left: 50%;