Oilpan: Ensure that classes with virtual trace methods always have vtables for their left-most base…

Source/core/html/canvas/WebGLRenderingContextBase.cpp

Index: Source/core/html/canvas/WebGLRenderingContextBase.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContextBase.cpp b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
index a0a2d94ebcc9f2a8ba50ff73138c7279c658d4ab..443ea1befc0b6a1e0607c12f066ad9adefad92ea 100644
--- a/Source/core/html/canvas/WebGLRenderingContextBase.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
@@ -502,7 +502,7 @@ public:
 
     virtual void onContextLost() { m_context->forceLostContext(WebGLRenderingContextBase::RealLostContext); }
 
-    void trace(Visitor* visitor)
+    virtual void trace(Visitor* visitor)
     {
         visitor->trace(m_context);
     }
@@ -531,7 +531,7 @@ public:
         InspectorInstrumentation::didFireWebGLErrorOrWarning(m_context->canvas(), message);
     }
 
-    void trace(Visitor* visitor)
+    virtual void trace(Visitor* visitor)
     {
         visitor->trace(m_context);
     }