ozone: Introduce ClientPixmap and ClientPixmapFactory for non-GPU processes.

content/child/BUILD.gn

Index: content/child/BUILD.gn
diff --git a/content/child/BUILD.gn b/content/child/BUILD.gn
index b2e978aa48695896eb0687b358b7209ae02713a9..5a73f5ad97f79adc249254ea26d4b7b0f8ef6cf1 100644
--- a/content/child/BUILD.gn
+++ b/content/child/BUILD.gn
@@ -132,4 +132,11 @@ source_set("child") {
   if (is_win || !use_aura) {
     sources -= [ "npapi/webplugin_delegate_impl_aura.cc" ]
   }
+
+  if (!use_ozone) {
+    sources -= [
+      "child_native_pixmap_manager_ozone.cc",
+      "child_native_pixmap_manager_ozone.h",
+    ]
+  }
 }