Add [CachedAccessor] attribute to cache (almost) constant accessors (window.document).

third_party/WebKit/Source/bindings/core/v8/WindowProxy.h

Index: third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
index 0765d0248a94b16ec8c1df89d0ba7088962a4463..1e92c59e30e9f5ff27589d7270de8a41624c5875 100644
--- a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
+++ b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.h
@@ -40,6 +40,7 @@
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 #include "wtf/text/AtomicString.h"
+#include <map>
 #include <v8.h>
 
 namespace blink {
@@ -85,6 +86,15 @@ public:
 
     DOMWrapperWorld& world() { return *m_world; }
 
+    // Global map, 'name' -> private property for all cached accessors.
+    typedef std::map<std::string, v8::Eternal<v8::Private>> StringPrivateMap;
+    static StringPrivateMap& cachedAccessors()
+    {
+        DCHECK(isMainThread());

[jochen (gone - plz use gerrit), 2016/09/15 08:20:51]

that means that this feature is currently not available to workers, but since
it's on window proxy that's fine I guess

[jochen (gone - plz use gerrit), 2016/09/15 08:20:51]

that means that this feature is currently not available to workers, but since
it's on window proxy that's fine I guess

[Alfonso, 2016/09/16 14:21:48]

Refactor to use V8PrivateProperty to expose private properties, this is no
longer needed/used.

+        DEFINE_STATIC_LOCAL(StringPrivateMap, map, ());

[haraken, 2016/09/15 09:26:10]

If this map is intended to be per-isolate, can you put the map on
V8PerIsolateData? WindowProxy doesn't look like a right place to put it.

That said, as yukishiino@ mentioned, if you can use V8PrivateProperty, that will
be the best solution.

[Alfonso, 2016/09/16 14:21:48]

Done.

+        return map;
+    }
+
 private:
     WindowProxy(Frame*, PassRefPtr<DOMWrapperWorld>, v8::Isolate*);
     bool initialize();