Give the media context small memory limits (same as compositor).

gpu/command_buffer/client/shared_memory_limits.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_SHARED_MEMORY_LIMITS_H_
 #define GPU_COMMAND_BUFFER_CLIENT_SHARED_MEMORY_LIMITS_H_
 
 #include <stddef.h>
 
 namespace gpu {
 
 struct SharedMemoryLimits {
   int32_t command_buffer_size = 1024 * 1024;
   uint32_t start_transfer_buffer_size = 1 * 1024 * 1024;
   uint32_t min_transfer_buffer_size = 1 * 256 * 1024;
   uint32_t max_transfer_buffer_size = 16 * 1024 * 1024;
 
   static constexpr uint32_t kNoLimit = 0;
   uint32_t mapped_memory_reclaim_limit = kNoLimit;
+
+  // These are limits for contexts only used for creating textures, mailboxing
+  // them and dealing with synchronization.
+  static SharedMemoryLimits ForMailboxContext() {
+    SharedMemoryLimits limits;
+    limits.command_buffer_size = 64 * 1024;
+    limits.start_transfer_buffer_size = 64 * 1024;
+    limits.min_transfer_buffer_size = 64 * 1024;
+    return limits;
+  }
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_SHARED_MEMORY_LIMITS_H_