Oilpan: GC_TRACING: Improve object path dump

We frequently saw object path dump like:

    Path to 1d6ec5d8 of WebCore::Node
    <- 7abc4660 of Persistent

Then, we needed to investigate what this Persistent is. It took much time.

This CL introduces 'tracing name' property to Persistent if
ENABLE(GC_TRACING). The property is automatically filled with
backtrace of a Persistent constructor. We'll get dump like:

    Path to 1bd56220 of WebCore::Node
    <- 1bd55ff8 of WebCore::Node
    <- 1bd55dc8 of WebCore::Node
    <- 7d046600 of Persistent ... Backtrace:
            Persistent<HTMLSelectElement, ThreadLocalPersistents<(ThreadAffinity)1> >::Persistent(HTMLSelectElement*)
            v8::Handle<v8::Object> V8DOMWrapper::associateObjectWithWrapper<V8HTMLSelectElement, HTMLSelectElement>(HTMLSelectElement*, WrapperTypeInfo const*, v8::Handle<v8::Object>, v8::Isolate*, WrapperConfiguration::Lifetime)
            v8::Handle<v8::Object> V8DOMWrapper::associateObjectWithWrapper<V8HTMLSelectElement, HTMLSelectElement>(WTF::RawPtr<HTMLSelectElement>, WrapperTypeInfo const*, v8::Handle<v8::Object>, v8::Isolate*, WrapperConfiguration::Lifetime)
            V8HTMLSelectElement::createWrapper(WTF::RawPtr<HTMLSelectElement>, v8::Handle<v8::Object>, v8::Isolate*)

Additional improvement of the object path dump:
* Correct host info name for heap collections
* Don't try to dump unknown objects.

BUG=

Review URL: https://codereview.chromium.org/337653002

git-svn-id: svn://svn.chromium.org/blink/trunk@176185 bbb929c8-8fbe-4397-9dbb-9b2b20218538