Oilpan: Fix compile after r200678.

Source/core/inspector/V8DebuggerAgent.h

Index: Source/core/inspector/V8DebuggerAgent.h
diff --git a/Source/core/inspector/V8DebuggerAgent.h b/Source/core/inspector/V8DebuggerAgent.h
index b7ba3625b0eeac2090281a9bb0f3e37b8ed041e6..1e604f4f38d8848b541bbd48698bce17c59441df 100644
--- a/Source/core/inspector/V8DebuggerAgent.h
+++ b/Source/core/inspector/V8DebuggerAgent.h
@@ -39,11 +39,13 @@ class V8Debugger;
 typedef String ErrorString;
 
 class CORE_EXPORT V8DebuggerAgent
-    : public V8DebuggerListener
+    : public NoBaseWillBeGarbageCollectedFinalized<V8DebuggerAgent>

[yurys, 2015/08/18 18:45:55]

This class is going to be moved out of Blink and cannot depend on Oilpan. Can we
start removing such dependencies now to avoid double work of first adding Oilpan
support for them just to remove it later?

[haraken, 2015/08/18 23:50:28]

I'm fine with it as long as you don't break oilpan builds. We had to land this
CL to fix the breakage.

+    , public V8DebuggerListener
     , public InspectorBackendDispatcher::DebuggerCommandHandler
     , public PromiseTracker::Listener {
     WTF_MAKE_NONCOPYABLE(V8DebuggerAgent);
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED(V8DebuggerAgent);
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(V8DebuggerAgent);
 public:
     enum BreakpointSource {
         UserBreakpointSource,
@@ -65,6 +67,7 @@ public:
 
     V8DebuggerAgent(InjectedScriptManager*, V8Debugger*, Client*, int contextGroupId);
     ~V8DebuggerAgent() override;
+    DECLARE_TRACE();
 
     void setInspectorState(InspectorState* state) { m_state = state; }
     void setFrontend(InspectorFrontend::Debugger* frontend) { m_frontend = frontend; }