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..ae9bd9d1b436a0c9c1002640f1fba899206e13fe 100644
--- a/content/browser/webui/shared_resources_data_source.cc
+++ b/content/browser/webui/shared_resources_data_source.cc
@@ -6,12 +6,14 @@
 
 #include <stddef.h>
 
+#include "base/bind.h"
 #include "base/containers/hash_tables.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #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"
@@ -69,6 +71,20 @@ const ResourcesMap& GetResourcesMap() {
   return *resources_map;
 }
 
+scoped_refptr<base::RefCountedMemory> GetResourceBytesOnUIThread(int idr) {
+  if (idr == IDR_WEBUI_CSS_TEXT_DEFAULTS) {
+    std::string css = webui::GetWebUiCssTextDefaults();
+    return base::RefCountedString::TakeString(&css);
+  }
+
+  if (idr == IDR_WEBUI_CSS_TEXT_DEFAULTS_MD) {
+    std::string css = webui::GetWebUiCssTextDefaultsMd();
+    return base::RefCountedString::TakeString(&css);
+  }
+
+  return GetContentClient()->GetDataResourceBytes(idr);
+}
+
 }  // namespace
 
 SharedResourcesDataSource::SharedResourcesDataSource() {
@@ -89,19 +105,10 @@ void SharedResourcesDataSource::StartDataRequest(
   auto it = resources_map.find(path);
   int idr = (it != resources_map.end()) ? it->second : -1;
   DCHECK_NE(-1, idr) << " path: " << path;
-  scoped_refptr<base::RefCountedMemory> bytes;
-
-  if (idr == IDR_WEBUI_CSS_TEXT_DEFAULTS) {
-    std::string css = webui::GetWebUiCssTextDefaults();
-    bytes = base::RefCountedString::TakeString(&css);
-  } else if (idr == IDR_WEBUI_CSS_TEXT_DEFAULTS_MD) {
-    std::string css = webui::GetWebUiCssTextDefaultsMd();
-    bytes = base::RefCountedString::TakeString(&css);
-  } else {
-    bytes = GetContentClient()->GetDataResourceBytes(idr);
-  }
 
-  callback.Run(bytes.get());
+  BrowserThread::PostTaskAndReplyWithResult(
+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&GetResourceBytesOnUIThread, idr), callback);
 }
 
 std::string SharedResourcesDataSource::GetMimeType(