Plugin Power Saver: Add missing RenderFrame null-checks in placeholders

PluginPlaceholders are RenderFrameObservers, and render_frames can
go away before the object is actually destructed (during shutdown).

This CL adds the missing null checks needed to prevent trying to use
null pointers.

BUG=693120
R=raymes@chromium.org

Review-Url: https://codereview.chromium.org/2845413002 .
Cr-Commit-Position: refs/heads/master@{#468451}

chrome/renderer/plugins/chrome_plugin_placeholder.cc

@@ -233,6 +233,9 @@ void ChromePluginPlaceholder::PluginListChanged() {
   if (!GetFrame() || !plugin())
     return;
 
+  // Checking with GetFrame() is equivalent to checking render_frame().
+  DCHECK(render_frame());
+
   ChromeViewHostMsg_GetPluginInfo_Output output;
   std::string mime_type(GetPluginParams().mime_type.Utf8());
   render_frame()->Send(new ChromeViewHostMsg_GetPluginInfo(
@@ -289,6 +292,8 @@ void ChromePluginPlaceholder::ShowContextMenu(
     const blink::WebMouseEvent& event) {
   if (context_menu_request_id_)
     return;  // Don't allow nested context menu requests.
+  if (!render_frame())
+    return;
 
   content::ContextMenuParams params;
 
@@ -361,6 +366,7 @@ blink::WebPlugin* ChromePluginPlaceholder::CreatePlugin() {
 }
 
 void ChromePluginPlaceholder::OnBlockedTinyContent() {
+  DCHECK(render_frame());
   if (did_send_blocked_content_notification_)
     return;
 

components/plugins/renderer/loadable_plugin_placeholder.cc

@@ -41,6 +41,7 @@ void LoadablePluginPlaceholder::BlockForPowerSaverPoster() {
   DCHECK(!is_blocked_for_power_saver_poster_);
   is_blocked_for_power_saver_poster_ = true;
 
+  DCHECK(render_frame());
   render_frame()->RegisterPeripheralPlugin(
       url::Origin(GURL(GetPluginParams().url)),
       base::Bind(&LoadablePluginPlaceholder::MarkPluginEssential,
@@ -181,6 +182,8 @@ v8::Local<v8::Object> LoadablePluginPlaceholder::GetV8ScriptableObject(
 void LoadablePluginPlaceholder::OnUnobscuredRectUpdate(
     const gfx::Rect& unobscured_rect) {
   DCHECK(content::RenderThread::Get());
+  if (!render_frame())
+    return;
 
   if (!plugin() || !finished_loading_)
     return;