Store the profiler in the context instead of a thread-local variable (#1364)

lib/liquid/profiler/hooks.rb

@@ -3,10 +3,25 @@
 module Liquid
   module BlockBodyProfilingHook
     def render_node(context, output, node)
-      Profiler.profile_node_render(node, context.template_name) do
+      if (profiler = context.profiler)
+        profiler.profile_node(node, context.template_name) do
+          super
+        end
+      else
         super
       end
     end
   end
   BlockBody.prepend(BlockBodyProfilingHook)
+
+  module ContextProfilingHook
+    attr_accessor :profiler
+
+    def new_isolated_subcontext
+      new_context = super
+      new_context.profiler = profiler
+      new_context
+    end
+  end
+  Context.prepend(ContextProfilingHook)
 end