Omptimisation on layout and measure children of YogaLayout

Summary:
You must measure children before you lay them out, and YogaLayout didn't do this.  This fixes that.

We also only recompute the yoga tree if the YogaLayout is laid out with a different size to what it's been measured as.

Reviewed By: emilsjolander

Differential Revision: D4572237

fbshipit-source-id: 6e86dbf939b06338c1dc2a37b7dafafd548dd390

android/src/main/java/com/facebook/yoga/android/YogaLayout.java

@@ -260,6 +260,13 @@ public class YogaLayout extends ViewGroup {
       if (view.getVisibility() == GONE) {
         return;
       }
+      view.measure(
+          View.MeasureSpec.makeMeasureSpec(
+              Math.round(node.getLayoutWidth()),
+              View.MeasureSpec.EXACTLY),
+          View.MeasureSpec.makeMeasureSpec(
+              Math.round(node.getLayoutHeight()),
+              View.MeasureSpec.EXACTLY));
       view.layout(
           Math.round(xOffset + node.getLayoutX()),
           Math.round(yOffset + node.getLayoutY()),
@@ -286,10 +293,12 @@ public class YogaLayout extends ViewGroup {
   protected void onLayout(boolean changed, int l, int t, int r, int b) {
     // Either we are a root of a tree, or this function is called by our parent's onLayout, in which
     // case our r-l and b-t are the size of our node.
-    if (!(getParent() instanceof YogaLayout)) {
-      createLayout(
-          MeasureSpec.makeMeasureSpec(r - l, MeasureSpec.EXACTLY),
-          MeasureSpec.makeMeasureSpec(b - t, MeasureSpec.EXACTLY));
+    if (!(getParent() instanceof YogaLayout) &&
+        Math.round(mYogaNode.getLayoutHeight()) != b-t &&
+        Math.round(mYogaNode.getLayoutWidth()) != r-l) {
+        createLayout(
+            MeasureSpec.makeMeasureSpec(r - l, MeasureSpec.EXACTLY),
+            MeasureSpec.makeMeasureSpec(b - t, MeasureSpec.EXACTLY));
     }
 
     applyLayoutRecursive(mYogaNode, 0, 0);