Add an assert that TracedValue builder closes only most recently opened container

Source/platform/TracedValue.h

Index: Source/platform/TracedValue.h
diff --git a/Source/platform/TracedValue.h b/Source/platform/TracedValue.h
index 23f3ae5f81be8e323ad688f505a6b345026eda9c..7f751054ea92aa7eb122d661a48432df1af53eb5 100644
--- a/Source/platform/TracedValue.h
+++ b/Source/platform/TracedValue.h
@@ -50,6 +50,7 @@ class TracedDictionary : public TracedValueBase {
 public:
     OwnerType& endDictionary()
     {
+        ASSERT(m_stack.size() == nestingLevel);
         endCurrentDictionary();
         return *reinterpret_cast<OwnerType*>(this);
     }
@@ -85,6 +86,8 @@ public:
         return *this;
     }
 
+    static const size_t nestingLevel = OwnerType::nestingLevel + 1;
+
 private:
     TracedDictionary();
     ~TracedDictionary();
@@ -106,6 +109,7 @@ public:
     }
     OwnerType& endArray()
     {
+        ASSERT(m_stack.size() == nestingLevel);
         endCurrentArray();
         return *reinterpret_cast<OwnerType*>(this);
     }
@@ -131,6 +135,8 @@ public:
         return *this;
     }
 
+    static const size_t nestingLevel = OwnerType::nestingLevel + 1;
+
 private:
     TracedArray();
     ~TracedArray();
@@ -165,6 +171,8 @@ public:
         return *this;
     }
     PassRefPtr<TraceEvent::ConvertableToTraceFormat> finish();
+
+    static const size_t nestingLevel = 1;
 };
 
 } // namespace WebCore