Make ModuleSystem have a const view of ResourceBundleSourceMap.

extensions/renderer/module_system_test.cc

Index: extensions/renderer/module_system_test.cc
diff --git a/extensions/renderer/module_system_test.cc b/extensions/renderer/module_system_test.cc
index 06a4d5590460f24d3ec457e47dbc07aa5772bf63..dcc37106d7a3fc0dbfc26e3a6d8c9e36aedb4d67 100644
--- a/extensions/renderer/module_system_test.cc
+++ b/extensions/renderer/module_system_test.cc
@@ -105,13 +105,14 @@ class ModuleSystemTestEnvironment::StringSourceMap
   ~StringSourceMap() override {}
 
   v8::Local<v8::Value> GetSource(v8::Isolate* isolate,
-                                 const std::string& name) override {
+                                 const std::string& name) const override {
     if (source_map_.count(name) == 0)

[Devlin, 2016/04/12 17:01:25]

Unrelated to this patch, but this is a double look-up.  Can we make this just
use find() from the start?

[lazyboy, 2016/04/12 17:29:28]

Good catch, thank you.
Done.

       return v8::Undefined(isolate);
-    return v8::String::NewFromUtf8(isolate, source_map_[name].c_str());
+    return v8::String::NewFromUtf8(isolate,
+                                   source_map_.find(name)->second.c_str());
   }
 
-  bool Contains(const std::string& name) override {
+  bool Contains(const std::string& name) const override {
     return source_map_.count(name);
   }