WebUI: Fix crash while loading scripts for webview.[add/remove]ContentScripts API.

extensions/browser/web_ui_user_script_loader.cc

Index: extensions/browser/web_ui_user_script_loader.cc
diff --git a/extensions/browser/web_ui_user_script_loader.cc b/extensions/browser/web_ui_user_script_loader.cc
index facbadb0ee2ed8f91890418bdd723eb0550b02aa..dd7550b3446f4b16482fe8ae4b73e1d6c310fd26 100644
--- a/extensions/browser/web_ui_user_script_loader.cc
+++ b/extensions/browser/web_ui_user_script_loader.cc
@@ -86,14 +86,20 @@ void WebUIUserScriptLoader::LoadScripts(
     int render_process_id = iter->second.render_process_id;
     int render_frame_id = iter->second.render_frame_id;
 
-    content::BrowserContext* browser_context =
-        content::RenderProcessHost::FromID(render_process_id)
-            ->GetBrowserContext();
-
-    CreateWebUIURLFetchers(script->js_scripts(), browser_context,
-                           render_process_id, render_frame_id);
-    CreateWebUIURLFetchers(script->css_scripts(), browser_context,
-                           render_process_id, render_frame_id);
+    content::RenderProcessHost* render_process_host =
+        content::RenderProcessHost::FromID(render_process_id);
+
+    // LoadScripts may not be synchronous with AddScripts. Hence the
+    // |render_process_host| may no longer be alive.

[lazyboy, 2017/05/22 23:34:53]

As we don't have a repro case, might be worth adding a TODO here to investigate
as I'm not sure if there's any side effect of this happening (e.g. other
assumptions might break somewhere else). WebUIWebViewBrowserTest has tests for
content scripts from webui webview, you might want to see if you can write a
test to repro this. If not, you can add that note to the TODO here.

[karandeepb, 2017/05/24 21:36:57]

Tryed adding a test in Patchset 2, but don't have a linux machine to verify it.
Adding a TODO.

+    if (render_process_host) {
+      content::BrowserContext* browser_context =
+          render_process_host->GetBrowserContext();
+
+      CreateWebUIURLFetchers(script->js_scripts(), browser_context,
+                             render_process_id, render_frame_id);
+      CreateWebUIURLFetchers(script->css_scripts(), browser_context,
+                             render_process_id, render_frame_id);
+    }
 
     script_render_info_map_.erase(script->id());
   }