Use mojo from the PDF extension instead of using an extension API.

extensions/renderer/module_system.cc

Index: extensions/renderer/module_system.cc
diff --git a/extensions/renderer/module_system.cc b/extensions/renderer/module_system.cc
index f3fdf5d3c1704eb7bf6ba387d9f2b23945755920..f577c53e4f568220229c47a16a837cbc60903753 100644
--- a/extensions/renderer/module_system.cc
+++ b/extensions/renderer/module_system.cc
@@ -169,12 +169,11 @@ ModuleSystem::ModuleSystem(ScriptContext* context, const SourceMap* source_map)
   SetPrivate(global, kModuleSystem, v8::External::New(isolate, this));
 
   gin::ModuleRegistry::From(context->v8_context())->AddObserver(this);
-  // TODO(devlin): We really shouldn't be injecting mojo into every blessed
-  // extension context - it's wasteful. But it's better than injecting into
-  // every frame (previous behavior) so start with this while we investigate
-  // further. See crbug.com/636655.
   if (context_->GetRenderFrame() &&
-      context_->context_type() == Feature::BLESSED_EXTENSION_CONTEXT) {
+      context_->context_type() == Feature::BLESSED_EXTENSION_CONTEXT &&
+      context_->GetAvailability("mojoPrivate").is_available()) {
+    gin::ModuleRegistry::InstallGlobals(context->isolate(),
+                                        context->v8_context()->Global());
     context_->GetRenderFrame()->EnsureMojoBuiltinsAreAvailable(
         context->isolate(), context->v8_context());
   }