Force layout and invalidation for new plugin content

Correct paint invalidation was not occurring for the plugin placeholder
content in Chromium when WebPluginContainer paint invalidation is
delayed until the paint invalidation phase of the document lifecycle.

Here we set the needs layout and needs full paint invalidation flags so that layout is re-done on the plugin content at the next opportunity.

Depends on Blink review https://codereview.chromium.org/1056893003

R=tommycli
BUG=472348

Review URL: https://codereview.chromium.org/1056643002

Cr-Commit-Position: refs/heads/master@{#324127}

components/plugins/renderer/loadable_plugin_placeholder.cc

@@ -329,6 +329,12 @@ void LoadablePluginPlaceholder::DidFinishLoadingCallback() {
   if (message_.length() > 0)
     UpdateMessage();
 
+  // Ensure that we force a layout and paint invalidation for the new
+  // content. This will cause the container invalidation to be acted upon.
+  blink::WebFrame* frame = GetFrame();
+  blink::WebView* view = frame->view();
+  view->setNeedsLayoutAndFullPaintInvalidation();
+
   // Wait for the placeholder to finish loading to hide the premade plugin.
   // This is necessary to prevent a flicker.
   if (premade_throttler_ && !placeholder_was_replaced_)