terminal: send mime types for terminal files

BUG=999950

Change-Id: Ia2e6e313824badc43ffb2eb68688c60171806cdb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1816003
Commit-Queue: Julian Watson <juwa@google.com>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Auto-Submit: Julian Watson <juwa@google.com>
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699180}

chrome/browser/ui/webui/chromeos/terminal/terminal_source.cc

@@ -71,3 +71,8 @@ std::string TerminalSource::GetMimeType(const std::string& path) {
     net::GetWellKnownMimeTypeFromExtension(ext.substr(1), &mime_type);
   return mime_type;
 }
+
+bool TerminalSource::ShouldServeMimeTypeAsContentTypeHeader() {
+  // TerminalSource pages include js modules which require an explicit MimeType.
+  return true;
+}

chrome/browser/ui/webui/chromeos/terminal/terminal_source.h

@@ -31,6 +31,8 @@ class TerminalSource : public content::URLDataSource {
 
   std::string GetMimeType(const std::string& path) override;
 
+  bool ShouldServeMimeTypeAsContentTypeHeader() override;
+
   DISALLOW_COPY_AND_ASSIGN(TerminalSource);
 };