compositor-worker: Share a thread and an isolate for compositor workers.

Source/modules/InitModules.cpp

Index: Source/modules/InitModules.cpp
diff --git a/Source/modules/InitModules.cpp b/Source/modules/InitModules.cpp
index 1cfa4148a3228f97f24be8da134577da668228f6..00523081697cfee078a181938cc02ca5de5b2256 100644
--- a/Source/modules/InitModules.cpp
+++ b/Source/modules/InitModules.cpp
@@ -13,6 +13,7 @@
 #include "modules/EventTargetModulesNames.h"
 #include "modules/IndexedDBNames.h"
 #include "modules/accessibility/AXObjectCacheImpl.h"
+#include "modules/compositorworker/CompositorWorkerManager.h"
 #include "modules/filesystem/DraggedIsolatedFileSystemImpl.h"
 #include "modules/webdatabase/DatabaseManager.h"
 
@@ -33,11 +34,15 @@ void ModulesInitializer::init()
 
     CoreInitializer::init();
 
+    if (RuntimeEnabledFeatures::compositorWorkerEnabled())
+        CompositorWorkerManager::initialize();
+
     ASSERT(isInitialized());
 }
 
 void ModulesInitializer::terminateThreads()
 {
+    CompositorWorkerManager::shutdown();
     DatabaseManager::terminateDatabaseThread();
 }