support display: -webkit-flex and -webkit-flex: 1

layout/style/nsCSSKeywordList.h

@@ -126,6 +126,7 @@ CSS_KEY(-moz-workspace, _moz_workspace)
 CSS_KEY(-moz-zoom-in, _moz_zoom_in)
 CSS_KEY(-moz-zoom-out, _moz_zoom_out)
 CSS_KEY(-webkit-box, _webkit_box)
+CSS_KEY(-webkit-flex, _webkit_flex)
 CSS_KEY(-webkit-inline-box, _webkit_inline_box)
 CSS_KEY(absolute, absolute)
 CSS_KEY(active, active)

layout/style/nsCSSParser.cpp

@@ -7047,6 +7047,12 @@ CSSParserImpl::LookupKeywordPrefixAware(nsAString& aKeywordStr,
       return (keyword == eCSSKeyword__moz_box) ?
         eCSSKeyword_flex : eCSSKeyword_inline_flex;
     }
+
+    if (keyword == eCSSKeyword__webkit_flex) {
+      if (sWebkitPrefixedAliasesEnabled || ShouldUseUnprefixingService()) {
+        return eCSSKeyword_flex;
+      }
+    }
   }
 
   return keyword;

layout/style/nsCSSPropAliasList.h

@@ -323,6 +323,11 @@ CSS_PROP_ALIAS(-webkit-box-sizing,
                WebkitBoxSizing,
                WEBKIT_PREFIX_PREF)
 
+CSS_PROP_ALIAS(-webkit-flex,
+               flex,
+               WebkitFlex,
+               WEBKIT_PREFIX_PREF)
+
 // Alias -webkit-box properties to their -moz-box equivalents.
 // (NOTE: Even though they're aliases, in practice these -webkit properties
 // will behave a bit differently from their -moz versions, if they're

layout/style/nsCSSProps.cpp

@@ -1284,8 +1284,9 @@ KTableEntry nsCSSProps::kDisplayKTable[] = {
   // The next two entries are controlled by the layout.css.grid.enabled pref.
   { eCSSKeyword_grid,                NS_STYLE_DISPLAY_GRID },
   { eCSSKeyword_inline_grid,         NS_STYLE_DISPLAY_INLINE_GRID },
-  // The next two entries are controlled by the layout.css.prefixes.webkit pref.
+  // The next three entries are controlled by the layout.css.prefixes.webkit pref.
   { eCSSKeyword__webkit_box,         NS_STYLE_DISPLAY_WEBKIT_BOX },
+  { eCSSKeyword__webkit_flex,        NS_STYLE_DISPLAY_WEBKIT_FLEX },
   { eCSSKeyword__webkit_inline_box,  NS_STYLE_DISPLAY_WEBKIT_INLINE_BOX },
   // The next entry is controlled by the layout.css.display-contents.enabled
   // pref.

layout/style/nsStyleConsts.h

@@ -468,6 +468,7 @@ enum class FillMode : uint32_t;
 #define NS_STYLE_DISPLAY_CONTENTS               38
 #define NS_STYLE_DISPLAY_WEBKIT_BOX             39
 #define NS_STYLE_DISPLAY_WEBKIT_INLINE_BOX      40
+#define NS_STYLE_DISPLAY_WEBKIT_FLEX            41
 
 // See nsStyleDisplay
 // If these are re-ordered, nsComputedDOMStyle::DoGetContain() and