Enable shadow DOM-based "missing plugin" placeholder.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index e383c3fb31e6786bfcf02c00b74513d7d8eab17d..e422f3c130832ef3d5e657ec8809d8c15d1919cd 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -120,6 +120,7 @@
 #include "third_party/WebKit/public/web/WebNavigationPolicy.h"
 #include "third_party/WebKit/public/web/WebPlugin.h"
 #include "third_party/WebKit/public/web/WebPluginParams.h"
+#include "third_party/WebKit/public/web/WebPluginPlaceholder.h"
 #include "third_party/WebKit/public/web/WebRange.h"
 #include "third_party/WebKit/public/web/WebScriptSource.h"
 #include "third_party/WebKit/public/web/WebSearchableFormData.h"
@@ -1606,6 +1607,16 @@ void RenderFrameImpl::EnsureMojoBuiltinsAreAvailable(
 
 // blink::WebFrameClient implementation ----------------------------------------
 
+blink::WebPluginPlaceholder* RenderFrameImpl::createPluginPlaceholder(
+    blink::WebLocalFrame* frame,
+    const blink::WebPluginParams& params) {
+  DCHECK_EQ(frame_, frame);
+  return GetContentClient()
+      ->renderer()
+      ->CreatePluginPlaceholder(this, frame, params)
+      .release();
+}
+
 blink::WebPlugin* RenderFrameImpl::createPlugin(
     blink::WebLocalFrame* frame,
     const blink::WebPluginParams& params) {