[wrapper-tracing] Fix WebGL extension and attachment handling

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h

Index: third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h
diff --git a/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h b/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h
index a7b105741259c5e6c2394d39e2cb4c2884ff18e0..26cc9fb217b595707e80169a1a65e6390187e175 100644
--- a/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h
+++ b/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h
@@ -806,7 +806,8 @@ class MODULES_EXPORT WebGLRenderingContextBase : public CanvasRenderingContext,
     DraftExtension = 0x01,
   };
 
-  class ExtensionTracker : public GarbageCollected<ExtensionTracker> {
+  class ExtensionTracker : public GarbageCollected<ExtensionTracker>,
+                           public TraceWrapperBase {
    public:
     ExtensionTracker(ExtensionFlags flags, const char* const* prefixes)
         : m_draft(flags & DraftExtension), m_prefixes(prefixes) {}
@@ -872,17 +873,23 @@ class MODULES_EXPORT WebGLRenderingContextBase : public CanvasRenderingContext,
       ExtensionTracker::trace(visitor);
     }
 
+    DEFINE_INLINE_VIRTUAL_TRACE_WRAPPERS() {
+      visitor->traceWrappers(m_extension);
+    }
+
    private:
     TypedExtensionTracker(Member<T>& extensionField,
                           ExtensionFlags flags,
                           const char* const* prefixes)
-        : ExtensionTracker(flags, prefixes), m_extensionField(extensionField) {}
+        : ExtensionTracker(flags, prefixes),
+          m_extensionField(extensionField),
+          m_extension(this, nullptr) {}

[Michael Lippautz, 2016/11/30 21:07:38]

IIUC, then the TypedExtensionTracker should lazily create the extension, keep a
reference itself (which is the one we track for wrapper tracing), and announce
it to the parent reference provided.

[Ken Russell (switch to Gerrit), 2016/12/02 02:12:26]

Yes, I think that's right. Sorry for the complexity here. Some of this will be
changed in the fix for http://crbug.com/666061 / http://crbug.com/537054 .

 
     GC_PLUGIN_IGNORE("http://crbug.com/519953")
     Member<T>& m_extensionField;
     // ExtensionTracker holds it's own reference to the extension to ensure
     // that it is not deleted before this object's destructor is called
-    Member<T> m_extension;
+    TraceWrapperMember<T> m_extension;
   };
 
   bool m_extensionEnabled[WebGLExtensionNameCount];