Make ModuleSystem have a const view of ResourceBundleSourceMap.

extensions/renderer/module_system.cc

 // Copyright 2014 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 "extensions/renderer/module_system.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ skipping 121 matching lines @@
   }
 
   auto maybe = message->GetLineNumber(context_->v8_context());
   int line_number = maybe.IsJust() ? maybe.FromJust() : 0;
   return base::StringPrintf("%s:%d: %s",
                             resource_name.c_str(),
                             line_number,
                             error_message.c_str());
 }
 
-ModuleSystem::ModuleSystem(ScriptContext* context, SourceMap* source_map)
+ModuleSystem::ModuleSystem(ScriptContext* context, const SourceMap* source_map)
     : ObjectBackedNativeHandler(context),
       context_(context),
       source_map_(source_map),
       natives_enabled_(0),
       exception_handler_(new DefaultExceptionHandler(context)),
       weak_factory_(this) {
   RouteFunction(
       "require",
       base::Bind(&ModuleSystem::RequireForJs, base::Unretained(this)));
   RouteFunction(
@@ skipping 591 matching lines @@
 
 void ModuleSystem::ClobberExistingNativeHandler(const std::string& name) {
   NativeHandlerMap::iterator existing_handler = native_handler_map_.find(name);
   if (existing_handler != native_handler_map_.end()) {
     clobbered_native_handlers_.push_back(std::move(existing_handler->second));
     native_handler_map_.erase(existing_handler);
   }
 }
 
 }  // namespace extensions