Oilpan: Mention pre-finalizer registration in the documentation.

third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md

Index: third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md
diff --git a/third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md b/third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md
index c8febf225703afe852f3664c1049484291c6a0a1..0dc0c66326c6767d678670043ba1edf62ed81c04 100644
--- a/third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md
+++ b/third_party/WebKit/Source/platform/heap/BlinkGCAPIReference.md
@@ -98,10 +98,17 @@ with a destructor.
 
 A pre-finalizer must have the following function signature: `void preFinalizer()`. You can change the function name.
 
+A pre-finalizer must be registered in the constructor by using the following statement:
+"`ThreadState::current()->registerPreFinalizer(this, preFinalizerName);`".
+
 ```c++
 class YourClass : public GarbageCollectedFinalized<YourClass> {
     USING_PRE_FINALIZER(YourClass, dispose);
 public:
+    YourClass()
+    {
+        ThreadState::current()->registerPreFinalizer(this, dispose);

[sof, 2015/11/21 16:11:36]

ThreadState::registerPreFinalizer() doesn't take two arguments (any longer.)

[Yuta Kitamura, 2015/11/24 07:07:59]

Whoops, thanks. I'll follow-up with this.

(Comments in ThreadState.h also have two arguments version of this
 function, which I'll fix up together.)

+    }
     void dispose()
     {
         m_other->dispose(); // OK; you can touch other on-heap objects in a pre-finalizer.