Re-land: base: Implement browser process support for discardable memory.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 41137e503dd1d8923984bbeb6950c827312cda56..e53a8f4b2cb1735cb62d4036907fb9db8f57374b 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -656,8 +656,12 @@ void RenderThreadImpl::Init() {
 #endif
   }
 
-  base::DiscardableMemoryShmemAllocator::SetInstance(
-      ChildThreadImpl::discardable_shared_memory_manager());
+  // In single process, browser main loop set up the discardable memory
+  // allocator.
+  if (!command_line.HasSwitch(switches::kSingleProcess)) {
+    base::DiscardableMemoryShmemAllocator::SetInstance(
+        ChildThreadImpl::discardable_shared_memory_manager());
+  }
 
   service_registry()->AddService<RenderFrameSetup>(
       base::Bind(CreateRenderFrameSetup));