Make it possible to read CLD data from a file

chrome/browser/translate/translate_tab_helper.h

Index: chrome/browser/translate/translate_tab_helper.h
diff --git a/chrome/browser/translate/translate_tab_helper.h b/chrome/browser/translate/translate_tab_helper.h
index fb18ac1206dba116b0366e70180f98adcd1fe30d..e0581c4794edd25e7e02dda4bf1cb2bbfdbca072 100644
--- a/chrome/browser/translate/translate_tab_helper.h
+++ b/chrome/browser/translate/translate_tab_helper.h
@@ -8,6 +8,10 @@
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/platform_file.h"
+#include "base/synchronization/lock.h"
+#include "base/task_runner.h"
 #include "chrome/browser/ui/translate/translate_bubble_model.h"
 #include "components/translate/content/browser/content_translate_driver.h"
 #include "components/translate/core/common/translate_errors.h"
@@ -92,12 +96,38 @@ class TranslateTabHelper
                         const std::string& translated_lang,
                         TranslateErrors::Type error_type);
 
+  // Called when we receive ChromeViewHostMsg_NeedCLDData from a renderer.
+  // If we have already cached the data, responds immediately; else, enqueues
+  // a HandleCLDDataRequest on the blocking pool to cache the data.
+  // Acquires and releases s_file_lock_ in a non-blocking manner; queries
+  // handled while the file is being cached will gracefully and immediately
+  // fail.
+  void OnCLDDataRequested();
+
+  // Invoked on the blocking pool in order to cache the data. When successful,
+  // immediately responds to the request that initiated OnCLDDataRequested.
+  // Holds s_file_lock_ while the file is being cached.
+  void HandleCLDDataRequest();
+
+  // Sends the renderer a response containing the data file handle. No locking.
+  void SendCLDDataAvailable(const base::PlatformFile handle);
+
+  // Necessary for binding the callback to HandleCLDDataRequest on the blocking
+  // pool.
+  base::WeakPtrFactory<TranslateTabHelper> weak_pointer_factory_;
+
   // Shows the translate bubble.
   void ShowBubble(TranslateStep step, TranslateErrors::Type error_type);
 
   ContentTranslateDriver translate_driver_;
   scoped_ptr<TranslateManager> translate_manager_;
 
+  // The data file, cached as long as the process stays alive.
+  static base::PlatformFile s_cached_platform_file_; // guarded by file_lock_
+
+  // Guards s_cached_platform_file_
+  static base::Lock s_file_lock_;
+
   DISALLOW_COPY_AND_ASSIGN(TranslateTabHelper);
 };