Remove PluginLoadObserver and related logic, it was only used for NPAPI.

content/child/npapi/plugin_string_stream.cc

Index: content/child/npapi/plugin_string_stream.cc
diff --git a/content/child/npapi/plugin_string_stream.cc b/content/child/npapi/plugin_string_stream.cc
index 15f38adbf4f85b6cd761832a45be3b9df5c6e4a1..6bc1caffd3bddc9b333a2f0f24c8dcf067eb3f6b 100644
--- a/content/child/npapi/plugin_string_stream.cc
+++ b/content/child/npapi/plugin_string_stream.cc
@@ -10,10 +10,8 @@ namespace content {
 
 PluginStringStream::PluginStringStream(
     PluginInstance* instance,
-    const GURL& url,
-    bool notify_needed,
-    void* notify_data)
-    : PluginStream(instance, url.spec().c_str(), notify_needed, notify_data) {
+    const GURL& url)
+    : PluginStream(instance, url.spec().c_str()) {
 }
 
 PluginStringStream::~PluginStringStream() {