Dispose of DOMTimer upon explicit ExecutionContext unregistration.

Source/core/dom/ExecutionContext.cpp

Index: Source/core/dom/ExecutionContext.cpp
diff --git a/Source/core/dom/ExecutionContext.cpp b/Source/core/dom/ExecutionContext.cpp
index 23f4accad5d1ef752360d1a3de5642ed6c069d92..887f2e70ee4a597c20c5fe8596055cf0084bb9fb 100644
--- a/Source/core/dom/ExecutionContext.cpp
+++ b/Source/core/dom/ExecutionContext.cpp
@@ -205,6 +205,10 @@ void ExecutionContext::removeTimeoutByID(int timeoutID)
 {
     if (timeoutID <= 0)
         return;
+
+    if (DOMTimer* removedTimer = m_timeouts.get(timeoutID))
+        removedTimer->dispose();
+
     m_timeouts.remove(timeoutID);
 }