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

content/shell/tools/plugin/PluginTest.cpp

Index: content/shell/tools/plugin/PluginTest.cpp
diff --git a/content/shell/tools/plugin/PluginTest.cpp b/content/shell/tools/plugin/PluginTest.cpp
index d0a56c711e7a673711f3313be4a09a67ac6ce7b8..fa95d8911e9d1914d96bf0acf72896b2dc8d8ea5 100644
--- a/content/shell/tools/plugin/PluginTest.cpp
+++ b/content/shell/tools/plugin/PluginTest.cpp
@@ -135,16 +135,6 @@ NPError PluginTest::NPP_SetValue(NPNVariable, void* value) {
 
 // NPN functions.
 
-NPError PluginTest::NPN_GetURL(const char* url, const char* target) {
-  return browser->geturl(m_npp, url, target);
-}
-
-NPError PluginTest::NPN_GetURLNotify(const char* url,
-                                     const char* target,
-                                     void* notifyData) {
-  return browser->geturlnotify(m_npp, url, target, notifyData);
-}
-
 NPError PluginTest::NPN_GetValue(NPNVariable variable, void* value) {
   return browser->getvalue(m_npp, variable, value);
 }