gpu: Add out-of-line copy ctors for complex classes.

gpu/command_buffer/service/context_state.cc

Index: gpu/command_buffer/service/context_state.cc
diff --git a/gpu/command_buffer/service/context_state.cc b/gpu/command_buffer/service/context_state.cc
index 893465dc7250970c498fe2db8525e5713f137293..a430d1d8bcb0de3000f0cb09eb79c99a6e4b4412 100644
--- a/gpu/command_buffer/service/context_state.cc
+++ b/gpu/command_buffer/service/context_state.cc
@@ -87,6 +87,8 @@ TextureUnit::TextureUnit()
     : bind_target(GL_TEXTURE_2D) {
 }
 
+TextureUnit::TextureUnit(const TextureUnit& other) = default;
+
 TextureUnit::~TextureUnit() {
 }