Bug 1449736: Properly detect failure in receiving plugin NPObjects (r=jmathies)

We need to recognize IPDL errors in order to return the proper error status when the right PluginScriptableObject could not be found.

Differential Revision: https://phabricator.services.mozilla.com/D15469

--HG--
extra : moz-landing-system : lando

dom/plugins/ipc/PluginInstanceChild.cpp

@@ -268,14 +268,14 @@ int PluginInstanceChild::GetQuirks() {
 NPError PluginInstanceChild::InternalGetNPObjectForValue(NPNVariable aValue,
                                                          NPObject** aObject) {
   PluginScriptableObjectChild* actor = nullptr;
-  NPError result = NPERR_NO_ERROR;
+  NPError result = NPERR_GENERIC_ERROR;
 
   switch (aValue) {
     case NPNVWindowNPObject:
       if (!(actor = mCachedWindowActor)) {
         PPluginScriptableObjectChild* actorProtocol;
-        CallNPN_GetValue_NPNVWindowNPObject(&actorProtocol, &result);
-        if (result == NPERR_NO_ERROR) {
+        if (CallNPN_GetValue_NPNVWindowNPObject(&actorProtocol, &result) &&
+            (result == NPERR_NO_ERROR)) {
           actor = mCachedWindowActor =
               static_cast<PluginScriptableObjectChild*>(actorProtocol);
           NS_ASSERTION(actor, "Null actor!");
@@ -288,8 +288,8 @@ NPError PluginInstanceChild::InternalGetNPObjectForValue(NPNVariable aValue,
     case NPNVPluginElementNPObject:
       if (!(actor = mCachedElementActor)) {
         PPluginScriptableObjectChild* actorProtocol;
-        CallNPN_GetValue_NPNVPluginElementNPObject(&actorProtocol, &result);
-        if (result == NPERR_NO_ERROR) {
+        if (CallNPN_GetValue_NPNVPluginElementNPObject(&actorProtocol, &result) &&
+            (result == NPERR_NO_ERROR)) {
           actor = mCachedElementActor =
               static_cast<PluginScriptableObjectChild*>(actorProtocol);
           NS_ASSERTION(actor, "Null actor!");