Avoid touching ResourceBundle fonts from non-UI thread

content/browser/webui/shared_resources_data_source.cc

Index: content/browser/webui/shared_resources_data_source.cc
diff --git a/content/browser/webui/shared_resources_data_source.cc b/content/browser/webui/shared_resources_data_source.cc
index 03721b0c5e1d1d024c234d0ea0cc90f7f2c5a47a..c6bb694868e7d23722ef268e97c9732ac691982b 100644
--- a/content/browser/webui/shared_resources_data_source.cc
+++ b/content/browser/webui/shared_resources_data_source.cc
@@ -12,6 +12,7 @@
 #include "base/memory/ref_counted_memory.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
+#include "content/public/browser/browser_thread.h"
 #include "content/public/common/content_client.h"
 #include "content/public/common/url_constants.h"
 #include "ui/base/layout.h"
@@ -148,6 +149,10 @@ std::string SharedResourcesDataSource::GetMimeType(
 scoped_refptr<base::SingleThreadTaskRunner>
 SharedResourcesDataSource::TaskRunnerForRequestPath(
     const std::string& path) const {
+  // Use UI thread to load CSS since its construction touches non-thread-safe
+  // gfx::Font names in ui::ResourceBundle.
+  if (GetMimeType(path) == "text/css")
+    return BrowserThread::GetTaskRunnerForThread(BrowserThread::UI);

[Dan Beam, 2017/02/23 00:27:56]

sorry, don't do this

[Dan Beam, 2017/02/23 00:32:26]

and by that i mean, push all text/css to the UI thread.

also, should we just call the super?

... SharedResourcesDataSource::TaskRunnerForRequestPath(...) const {
  const ResourcesMap& resources = GetResourcesMap();
  auto it = resources.find(path);
  if (it != resources.end() &&
      (it->second == IDR_WEBUI_CSS_TEXT_DEFAULTS ||
       it->second == IDR_WEBUI_CSS_TEXT_DEFAULTS_MD)) {
    return URLDataSource::TaskRunnerForRequestPath(path);
  }
  return nullptr;
}

[tzik, 2017/02/23 00:58:19]

Updated.

[tzik, 2017/02/23 00:58:19]

Hmm, I think it's unclear from this code that the super class returns the UI
thread task runner. Can we take it from BrowserThread?

[Dan Beam, 2017/02/23 02:11:30]

i'm fine with either

   return nullptr;
 }