Add early-injection capability to user scripts. I haven't yet

chrome/browser/extensions/user_script_master.cc

 // Copyright (c) 2008 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.
 
 #include "chrome/browser/extensions/user_script_master.h"
 
 #include <vector>
 
 #include "base/file_path.h"
 #include "base/file_util.h"
@@ skipping 27 matching lines @@
   // http://wiki.greasespot.net/Metadata_block
   StringPiece line;
   size_t line_start = 0;
   size_t line_end = 0;
   bool in_metadata = false;
 
   static const StringPiece kUserScriptBegin("// ==UserScript==");
   static const StringPiece kUserScriptEng("// ==/UserScript==");
   static const StringPiece kIncludeDeclaration("// @include ");
   static const StringPiece kMatchDeclaration("// @match ");
+  static const StringPiece kRunAtDeclaration("// @run-at ");
+  static const StringPiece kRunAtDocumentStartValue("document-start");
+  static const StringPiece kRunAtDocumentEndValue("document-end");
 
   while (line_start < script_text.length()) {
     line_end = script_text.find('\n', line_start);
 
     // Handle the case where there is no trailing newline in the file.
     if (line_end == std::string::npos) {
       line_end = script_text.length() - 1;
     }
 
     line.set(script_text.data() + line_start, line_end - line_start);
@@ skipping 11 matching lines @@
       if (GetDeclarationValue(line, kIncludeDeclaration, &value)) {
         // We escape some characters that MatchPattern() considers special.
         ReplaceSubstringsAfterOffset(&value, 0, "\\", "\\\\");
         ReplaceSubstringsAfterOffset(&value, 0, "?", "\\?");
         script->add_glob(value);
       } else if (GetDeclarationValue(line, kMatchDeclaration, &value)) {
         URLPattern pattern;
         if (!pattern.Parse(value))
           return false;
         script->add_url_pattern(pattern);
+      } else if (GetDeclarationValue(line, kRunAtDeclaration, &value)) {
+        if (value == kRunAtDocumentStartValue)
+          script->set_run_location(UserScript::DOCUMENT_START);
+        else if (value != kRunAtDocumentEndValue)
+          return false;
       }
 
       // TODO(aa): Handle more types of metadata.
     }
 
     line_start = line_end + 1;
   }
 
   // It is probably a mistake to declare both @include and @match rules.
   if (script->globs().size() > 0 && script->url_patterns().size() > 0)
@@ skipping 173 matching lines @@
 
   StartScan();
 }
 
 void UserScriptMaster::StartScan() {
   if (!script_reloader_)
     script_reloader_ = new ScriptReloader(this);
 
   script_reloader_->StartScan(worker_loop_, user_script_dir_, lone_scripts_);
 }