gpu: Add default constructor to SharedMemoryLimits.

gpu/command_buffer/client/shared_memory_limits.h

Index: gpu/command_buffer/client/shared_memory_limits.h
diff --git a/gpu/command_buffer/client/shared_memory_limits.h b/gpu/command_buffer/client/shared_memory_limits.h
index de821732696f4bc0270c05f961b6e3428f8f6e47..53881de0dc134d1be69fd7e3bd6ce7b9c10db361 100644
--- a/gpu/command_buffer/client/shared_memory_limits.h
+++ b/gpu/command_buffer/client/shared_memory_limits.h
@@ -10,6 +10,8 @@
 namespace gpu {
 
 struct SharedMemoryLimits {
+  SharedMemoryLimits() = default;
+
   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;