DevTools: serve MimeType as ContentType for debug_devtools

- Adds ShouldServeMimeTypeAsContentTypeHeader() on URLRequestFileJob
- With debug_devtools, our interceptor now serves files with
  ContentType header, allowing DevTools to importScripts() on
  locally-served bundled files.
- Without this CL, strict MIME-type checks prevent importScripts()
  in FormatterWorker, required for pretty-print and autocomplete.

Bug: 882013
Change-Id: Ib61284cfccd430dd9a4ddae769a416147c504e05
Reviewed-on: https://chromium-review.googlesource.com/1214365Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589944}

chrome/browser/profiles/profile_io_data.cc

@@ -267,12 +267,15 @@ class DebugDevToolsInterceptor : public net::URLRequestInterceptor {
       net::URLRequest* request,
       net::NetworkDelegate* network_delegate) const override {
     base::FilePath path;
-    if (IsSupportedDevToolsURL(request->url(), &path))
-      return new net::URLRequestFileJob(
+    if (IsSupportedDevToolsURL(request->url(), &path)) {
+      net::URLRequestFileJob* job = new net::URLRequestFileJob(
           request, network_delegate, path,
           base::CreateTaskRunnerWithTraits(
               {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
                base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN}));
+      job->ShouldServeMimeTypeAsContentTypeHeader();
+      return job;
+    }
 
     return NULL;
   }

net/url_request/url_request_file_job.cc

@@ -23,6 +23,7 @@
 #include "base/compiler_specific.h"
 #include "base/files/file_util.h"
 #include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
 #include "base/task_runner.h"
 #include "base/threading/thread_restrictions.h"
@@ -178,6 +179,17 @@ void URLRequestFileJob::SetExtraRequestHeaders(
   }
 }
 
+void URLRequestFileJob::GetResponseInfo(HttpResponseInfo* info) {
+  if (!serve_mime_type_as_content_type_ || !meta_info_.mime_type_result)
+    return;
+  auto headers =
+      base::MakeRefCounted<net::HttpResponseHeaders>("HTTP/1.1 200 OK");
+  headers->AddHeader(base::StringPrintf("%s: %s",
+                                        net::HttpRequestHeaders::kContentType,
+                                        meta_info_.mime_type.c_str()));
+  info->headers = headers;
+}
+
 void URLRequestFileJob::OnOpenComplete(int result) {}
 
 void URLRequestFileJob::OnSeekComplete(int64_t result) {}

net/url_request/url_request_file_job.h

@@ -46,6 +46,10 @@ class NET_EXPORT URLRequestFileJob : public URLRequestJob {
                           bool* insecure_scheme_was_upgraded) override;
   bool GetMimeType(std::string* mime_type) const override;
   void SetExtraRequestHeaders(const HttpRequestHeaders& headers) override;
+  void ShouldServeMimeTypeAsContentTypeHeader() {
+    serve_mime_type_as_content_type_ = true;
+  };
+  void GetResponseInfo(HttpResponseInfo* info) override;
 
   // An interface for subclasses who wish to monitor read operations.
   //
@@ -124,6 +128,7 @@ class NET_EXPORT URLRequestFileJob : public URLRequestJob {
   std::vector<HttpByteRange> byte_ranges_;
   HttpByteRange byte_range_;
   int64_t remaining_bytes_;
+  bool serve_mime_type_as_content_type_ = false;
 
   Error range_parse_result_;