Add support for WRAP_CONTENT to react views.

Summary: Fixes needing to specify exact height of react views in Mason.  Uses a ViewTreeObserver to delay draw until we have correct bounds.

Reviewed By: sriramramani

Differential Revision: D3527122

ReactAndroid/src/main/java/com/facebook/react/flat/FlatMeasuredViewGroup.java

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.flat;
+
+import android.graphics.Rect;
+
+/**
+ * Helper interface to provide measuring of FlatViewGroup when needed.  We don't override onMeasure
+ * for FlatViewGroup, which means that draw commands don't contributed to the measured width and
+ * height.  This allows us to expose our calculated dimensions taking into account draw commands,
+ * without changing the visibility of the FlatViewGroup.
+ */
+public interface FlatMeasuredViewGroup {
+  /**
+   * @return A rect consisting of the left, top, right, and bottommost edge among all children,
+   *   including draw commands.
+   */
+  Rect measureWithCommands();
+}

ReactAndroid/src/main/java/com/facebook/react/flat/FlatViewGroup.java

@@ -48,7 +48,7 @@ import com.facebook.react.views.view.ReactClippingViewGroupHelper;
  */
 /* package */ final class FlatViewGroup extends ViewGroup
     implements ReactInterceptingViewGroup, ReactClippingViewGroup,
-    ReactCompoundViewGroup, ReactPointerEventsView {
+    ReactCompoundViewGroup, ReactPointerEventsView, FlatMeasuredViewGroup {
   /**
    * Helper class that allows AttachDetachListener to invalidate the hosting View.
    */
@@ -543,6 +543,37 @@ import com.facebook.react.views.view.ReactClippingViewGroupHelper;
     LAYOUT_REQUESTS.clear();
   }
 
+  // Helper method for measure functionality provided by MeasuredViewGroup.
+  @Override
+  public Rect measureWithCommands() {
+    int childCount = getChildCount();
+    if (childCount == 0 && mDrawCommands.length == 0) {
+      return new Rect(0, 0, 0, 0);
+    }
+    int left = Integer.MAX_VALUE;
+    int top = Integer.MAX_VALUE;
+    int right = Integer.MIN_VALUE;
+    int bottom = Integer.MIN_VALUE;
+    for (int i = 0; i < childCount; i++) {
+      View child = getChildAt(i);
+      left = Math.min(left, child.getLeft());
+      top = Math.min(top, child.getTop());
+      right = Math.max(right, child.getRight());
+      bottom = Math.max(bottom, child.getBottom());
+    }
+    for (int i = 0; i < mDrawCommands.length; i++) {
+      if (!(mDrawCommands[i] instanceof AbstractDrawCommand)) {
+        continue;
+      }
+      AbstractDrawCommand drawCommand = (AbstractDrawCommand) mDrawCommands[i];
+      left = Math.min(left, Math.round(drawCommand.getLeft()));
+      top = Math.min(top, Math.round(drawCommand.getTop()));
+      right = Math.max(right, Math.round(drawCommand.getRight()));
+      bottom = Math.max(bottom, Math.round(drawCommand.getBottom()));
+    }
+    return new Rect(left, top, right, bottom);
+  }
+
   private @Nullable NodeRegion virtualNodeRegionWithinBounds(float touchX, float touchY) {
     for (int i = mNodeRegions.length - 1; i >= 0; --i) {
       NodeRegion nodeRegion = mNodeRegions[i];