gpu: Refactor memory buffer handling code out of content.

base/threading/thread_restrictions.h

Index: base/threading/thread_restrictions.h
diff --git a/base/threading/thread_restrictions.h b/base/threading/thread_restrictions.h
index 07b78aa9641e1ebdbfa80b69fd73ce8dd649ff73..0d5e588e953db43894e3744ba4547ed6affe7fde 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -52,6 +52,7 @@ class InFlightIO;
 }
 namespace gpu {
 class GpuChannelHost;
+class GpuHostMemoryBufferManager;
 }
 namespace mojo {
 class SyncCallRestrictions;
@@ -229,6 +230,7 @@ class BASE_EXPORT ThreadRestrictions {
   friend class disk_cache::BackendImpl;           // http://crbug.com/74623
   friend class disk_cache::InFlightIO;            // http://crbug.com/74623
   friend class gpu::GpuChannelHost;               // http://crbug.com/125264
+  friend class gpu::GpuHostMemoryBufferManager;   // http://crbug.com/125248
   friend class net::internal::AddressTrackerLinux;  // http://crbug.com/125097
   friend class net::NetworkChangeNotifierMac;     // http://crbug.com/125097
   friend class ::BrowserProcessImpl;              // http://crbug.com/125207