Move FieldTrialSynchronizer into content so it can be used by WebLayer
and other embedders.

There doesn't appear to be any existing tests for this functionality
and I'm not sure how to easily test it.

Bug: 1025612
Change-Id: I81354ff16a6bb9c9bc3a9ada99018ad1e2c82031
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1959034
Reviewed-by: Avi Drissman <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Commit-Queue: Alex Clarke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#737363}
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index f5f3e1a..a778a3b 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -105,6 +105,7 @@
 class RenderThreadObserver;
 class RendererBlinkPlatformImpl;
 class ResourceDispatcher;
+class VariationsRenderThreadObserver;
 
 #if defined(OS_ANDROID)
 class StreamTextureFactory;
@@ -612,6 +613,8 @@
 
   std::unique_ptr<viz::Gpu> gpu_;
 
+  std::unique_ptr<VariationsRenderThreadObserver> variations_observer_;
+
   scoped_refptr<base::SingleThreadTaskRunner>
       main_thread_compositor_task_runner_;