Remove ThreadStorage class in favour of thread_local

Summary:
#changelog: [internal]

When I built ThreadStorage I didn't know about existence of `thread_local` keyword. Because it achieves the same goal, using built in c++ features is preferred over building our own.

Reviewed By: JoshuaGross, shergin

Differential Revision: D24380680

fbshipit-source-id: e961fc34c6d3f085fc9b918b20bb4827de0d5624

ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp

@@ -12,7 +12,6 @@
 #include <react/renderer/core/LayoutContext.h>
 #include <react/renderer/debug/DebugStringConvertibleItem.h>
 #include <react/renderer/debug/SystraceSection.h>
-#include <react/utils/ThreadStorage.h>
 #include <yoga/Yoga.h>
 #include <algorithm>
 #include <limits>
@@ -21,6 +20,8 @@
 namespace facebook {
 namespace react {
 
+thread_local LayoutContext threadLocalLayoutContext;
+
 static void applyLayoutConstraints(
     YGStyle &yogaStyle,
     LayoutConstraints const &layoutConstraints) {
@@ -332,7 +333,7 @@ void YogaLayoutableShadowNode::layoutTree(
 
   applyLayoutConstraints(yogaNode_.getStyle(), layoutConstraints);
 
-  ThreadStorage<LayoutContext>::getInstance().set(layoutContext);
+  threadLocalLayoutContext = layoutContext;
 
   if (layoutContext.swapLeftAndRightInRTL) {
     swapLeftAndRightInTree(*this);
@@ -492,10 +493,8 @@ YGSize YogaLayoutableShadowNode::yogaNodeMeasureCallbackConnector(
       break;
   }
 
-  auto layoutContext = ThreadStorage<LayoutContext>::getInstance().get();
-
   auto size = shadowNodeRawPtr->measureContent(
-      layoutContext.value_or(LayoutContext{}), {minimumSize, maximumSize});
+      threadLocalLayoutContext, {minimumSize, maximumSize});
 
   return YGSize{yogaFloatFromFloat(size.width),
                 yogaFloatFromFloat(size.height)};