Web Inspector: Native Memory Instrumentation: reportLeaf method doesn't report the leaf node properly.
https://bugs.webkit.org/show_bug.cgi?id=109554

Source/WebCore:

In some cases leaves have no pointer so with the old schema we can't generate nodeId for them because we
can't insert 0 into hashmap. It happens when we call addPrivateBuffer method.

Drive by fix: I introduced a client interface for the HeapGraphSerializer.
It helps me to do the tests for the serializer.

Reviewed by Yury Semikhatsky.

It is covered by newly added tests in TestWebKitAPI.

* inspector/HeapGraphSerializer.cpp:
(WebCore::HeapGraphSerializer::HeapGraphSerializer):
(WebCore::HeapGraphSerializer::pushUpdate):
(WebCore::HeapGraphSerializer::reportNode):
(WebCore::HeapGraphSerializer::toNodeId):
(WebCore::HeapGraphSerializer::addRootNode):
* inspector/HeapGraphSerializer.h:
(HeapGraphSerializerClient):
(WebCore::HeapGraphSerializerClient::~HeapGraphSerializerClient):
(HeapGraphSerializer):
* inspector/InspectorMemoryAgent.cpp:
(WebCore::InspectorMemoryAgent::getProcessMemoryDistributionImpl):

Tools:

In some cases leaves have no pointer. As example when we report a leaf via addPrivateBuffer.
This patch has new set of tests for HeapGraphSerializer.

Reviewed by Yury Semikhatsky.

* TestWebKitAPI/TestWebKitAPI.gypi:
* TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj:
* TestWebKitAPI/Tests/WebCore/HeapGraphSerializerTest.cpp: Added.
* TestWebKitAPI/win/TestWebKitAPI.vcproj:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142618 268f45cc-cd09-0410-ab3c-d52691b4dbfc