Add a second format to the tracing json/begin_recording endpoint.

content/browser/tracing/tracing_ui.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_TRACING_TRACING_UI_H_
 #define CONTENT_BROWSER_TRACING_TRACING_UI_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "content/public/browser/trace_uploader.h"
 #include "content/public/browser/web_ui_controller.h"
 
+namespace base {
+namespace trace_event {
+class TraceConfig;
+}  // namespace trace_event
+}  // namespace base
+
 namespace content {
 
 class TracingDelegate;
 
 // The C++ back-end for the chrome://tracing webui page.
 class CONTENT_EXPORT TracingUI : public WebUIController {
  public:
   explicit TracingUI(WebUI* web_ui);
   ~TracingUI() override;
   void OnTraceUploadProgress(int64_t current, int64_t total);
   void OnTraceUploadComplete(bool success, const std::string& feedback);
 
+  // Public for testing.
+  static bool GetTracingOptions(const std::string& data64,

[Primiano Tucci (use gerrit), 2017/06/22 19:04:47]

static functions should go on the top. But also if this is the only change here,
not worth the hassle of another patchset.

[erikchen, 2017/06/22 19:30:45]

Done.

+                                base::trace_event::TraceConfig* trace_config);
+
  private:
   void DoUploadInternal(const std::string& file_contents,
                         TraceUploader::UploadMode upload_mode);
   void DoUpload(const base::ListValue* args);
   void DoUploadBase64Encoded(const base::ListValue* args);
 
   std::unique_ptr<TracingDelegate> delegate_;
   std::unique_ptr<TraceUploader> trace_uploader_;
   base::WeakPtrFactory<TracingUI> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TracingUI);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_TRACING_TRACING_UI_H_