[Extensions] Fix a data race in ChromeExtensionMessageFilter.

chrome/browser/renderer_host/chrome_extension_message_filter.cc

Index: chrome/browser/renderer_host/chrome_extension_message_filter.cc
diff --git a/chrome/browser/renderer_host/chrome_extension_message_filter.cc b/chrome/browser/renderer_host/chrome_extension_message_filter.cc
index 85891b1d32db5d30812f3d1b1c4933fd5278438d..00ddafb9de78af7b132cab4d1d973c74335b2956 100644
--- a/chrome/browser/renderer_host/chrome_extension_message_filter.cc
+++ b/chrome/browser/renderer_host/chrome_extension_message_filter.cc
@@ -28,8 +28,10 @@
 #include "extensions/browser/extension_system.h"
 #include "extensions/common/api/messaging/message.h"
 #include "extensions/common/extension_messages.h"
+#include "extensions/common/extension_set.h"
 #include "extensions/common/file_util.h"
 #include "extensions/common/manifest_handlers/default_locale_handler.h"
+#include "extensions/common/manifest_handlers/shared_module_info.h"
 #include "extensions/common/message_bundle.h"
 
 using content::BrowserThread;
@@ -199,24 +201,66 @@ void ChromeExtensionMessageFilter::OnPostMessage(
 
 void ChromeExtensionMessageFilter::OnGetExtMessageBundle(
     const std::string& extension_id, IPC::Message* reply_msg) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  const extensions::ExtensionSet& extension_set =
+      extension_info_map_->extensions();
+  const extensions::Extension* extension = extension_set.GetByID(extension_id);
+
+  if (!extension) {  // The extension has gone.
+    ExtensionHostMsg_GetMessageBundle::WriteReplyParams(
+        reply_msg, extensions::MessageBundle::SubstitutionMap());
+    Send(reply_msg);
+    return;
+  }
+
+  const std::string& default_locale =
+      extensions::LocaleInfo::GetDefaultLocale(extension);
+  if (default_locale.empty()) {
+    // A little optimization: send the answer here to avoid an extra thread hop.
+    std::unique_ptr<extensions::MessageBundle::SubstitutionMap> dictionary_map(
+        extensions::file_util::LoadNonLocalizedMessageBundleSubstitutionMap(
+            extension_id));
+    ExtensionHostMsg_GetMessageBundle::WriteReplyParams(reply_msg,
+                                                        *dictionary_map);
+    Send(reply_msg);
+    return;
+  }
+
+  std::vector<base::FilePath> paths_to_load;
+  paths_to_load.push_back(extension->path());
+
+  auto imports = extensions::SharedModuleInfo::GetImports(extension);
+  // Iterate through the imports in reverse.  This will allow later imported
+  // modules to override earlier imported modules, as the list order is
+  // maintained from the definition in manifest.json of the imports.
+  for (auto it = imports.rbegin(); it != imports.rend(); ++it) {
+    const extensions::Extension* imported_extension =
+        extension_set.GetByID(it->extension_id);
+    if (!imported_extension) {
+      NOTREACHED() << "Missing shared module " << it->extension_id;
+      continue;
+    }
+    paths_to_load.push_back(imported_extension->path());
+  }
+
   BrowserThread::PostBlockingPoolTask(
       FROM_HERE,
       base::Bind(
           &ChromeExtensionMessageFilter::OnGetExtMessageBundleOnBlockingPool,
-          this, extension_id, reply_msg));
+          this, paths_to_load, extension_id, default_locale, reply_msg));
 }
 
 void ChromeExtensionMessageFilter::OnGetExtMessageBundleOnBlockingPool(
-    const std::string& extension_id,
+    const std::vector<base::FilePath>& extension_paths,
+    const std::string& main_extension_id,
+    const std::string& default_locale,
     IPC::Message* reply_msg) {
   DCHECK(BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
 
-  const extensions::ExtensionSet& extension_set =
-      extension_info_map_->extensions();
-
   std::unique_ptr<extensions::MessageBundle::SubstitutionMap> dictionary_map(
-      extensions::file_util::LoadMessageBundleSubstitutionMapWithImports(
-          extension_id, extension_set));
+      extensions::file_util::LoadMessageBundleSubstitutionMapFromPaths(
+          extension_paths, main_extension_id, default_locale));
 
   ExtensionHostMsg_GetMessageBundle::WriteReplyParams(reply_msg,
                                                       *dictionary_map);