Add more out of line copy ctors for complex classes.

gpu/ipc/common/memory_stats.cc

Index: gpu/ipc/common/memory_stats.cc
diff --git a/gpu/ipc/common/memory_stats.cc b/gpu/ipc/common/memory_stats.cc
index af55e48b885e142fa9c0ed83244d9e7dd31aa0a0..5c8909ced6a3e74e2298bac8a5d57c5d81d1e97c 100644
--- a/gpu/ipc/common/memory_stats.cc
+++ b/gpu/ipc/common/memory_stats.cc
@@ -9,6 +9,9 @@ namespace gpu {
 VideoMemoryUsageStats::VideoMemoryUsageStats()
     : bytes_allocated(0), bytes_allocated_historical_max(0) {}
 
+VideoMemoryUsageStats::VideoMemoryUsageStats(
+    const VideoMemoryUsageStats& other) = default;
+
 VideoMemoryUsageStats::~VideoMemoryUsageStats() {}
 
 VideoMemoryUsageStats::ProcessStats::ProcessStats()