Add support for flex-grow, flex-shrink, and flex-basis

Summary: Add support for flex-grow, flex-shrink, and flex-basis properties. The flex property behavior is preserved for backwards compatibility.

Reviewed By: lucasr

Differential Revision: D3714520

fbshipit-source-id: 80d3a9a1e2b6f74b863bbe22357f2c9865fa290e

CSSLayout/CSSLayout-internal.h

@@ -33,7 +33,7 @@ typedef struct CSSLayout {
   float dimensions[2];
   CSSDirection direction;
 
-  float flexBasis;
+  float computedFlexBasis;
 
   // Instead of recomputing the entire layout every single time, we
   // cache some information to break early when nothing changed
@@ -57,7 +57,9 @@ typedef struct CSSStyle {
   CSSPositionType positionType;
   CSSWrapType flexWrap;
   CSSOverflow overflow;
-  float flex;
+  float flexGrow;
+  float flexShrink;
+  float flexBasis;
   float margin[6];
   float position[6];
   /**