Release Oilpan heap singletons prior to LSan leak detection.

third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp

Index: third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp b/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp
index ad829bc1d99588bb8d620d421d18e290daaddfbe..6eaed6ed024d1fd7b9cbc62d91725d709e859103 100644
--- a/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp
+++ b/third_party/WebKit/Source/core/css/CSSDefaultStyleSheets.cpp
@@ -68,7 +68,7 @@ static PassRefPtrWillBeRawPtr<StyleSheetContents> parseUASheet(const String& str
     sheet->parseString(str);
     // User Agent stylesheets are parsed once for the lifetime of the renderer
     // process and are intentionally leaked.
-    WTF_ANNOTATE_LEAKING_OBJECT_PTR(sheet.get());
+    LEAK_SANITIZER_IGNORE_OBJECT(sheet.get());

[haraken, 2015/12/07 14:46:10]

This is the only use case of WTF_ANNOTATE_LEAKING_OBJECT_PTR. Shall we just
replace it with LEAK_SANITIZER_DISABLED_SCOPE (and remove
WTF_ANNOTATE_LEAKING_OBJECT_PTR)?

[sof, 2015/12/07 15:09:28]

It is also used by Persistent*::registerAsStaticReference(), but those can be
avoided.

Actually, I'm not so sure we need to mark this object as individually ignored
here as all of these UA sheet objects belong to the
CSSDefaultStyleSheet::instance() singleton. Will investigate.

[sof, 2015/12/07 16:59:16]

Ah, this is just right as it is. The StyleSheetContents objects are reachable by
other objects, hence marking them as ignored is what's wanted. And marking the
object itself as ignored, rather than disabling LSan just for the duration of
its (initial) construction, will also let us not flag leaks against anything
that the object exclusively refers to at shutdown.

Same goes for Persistent*::registerAsStaticReference() uses, they're also
needed. Hence leaving this as it is.

     return sheet.release();
 }