Pass per-frame task runners to Workers (when possible) [2nd try]

third_party/WebKit/Source/core/dom/TaskRunnerHelper.h

Index: third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
diff --git a/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h b/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
index fb72520ea51694929384e84048ceeb3aaa307f7c..d475360a77cddc5c91fb7d4e199f8cb32bc03642 100644
--- a/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
+++ b/third_party/WebKit/Source/core/dom/TaskRunnerHelper.h
@@ -7,6 +7,7 @@
 
 #include "core/CoreExport.h"
 #include "wtf/Allocator.h"
+#include "wtf/HashTraits.h"
 
 namespace blink {
 
@@ -16,7 +17,7 @@ class LocalFrame;
 class ScriptState;
 class WebTaskRunner;
 
-enum class TaskType {
+enum class TaskType : unsigned {
     // Speced tasks and related internal tasks should be posted to one of
     // the following task runners. These task runners may be throttled.
     DOMManipulation,
@@ -43,6 +44,14 @@ enum class TaskType {
     Unthrottled,
 };
 
+// HashTraits for TaskType.
+struct TaskTypeTraits : WTF::GenericHashTraits<TaskType> {
+    static const bool emptyValueIsZero = false;
+    static TaskType emptyValue() { return static_cast<TaskType>(-1); }
+    static void constructDeletedValue(TaskType& slot, bool) { slot = static_cast<TaskType>(-2); }
+    static bool isDeletedValue(TaskType value) { return value == static_cast<TaskType>(-2); }
+};
+
 class CORE_EXPORT TaskRunnerHelper final {
     STATIC_ONLY(TaskRunnerHelper);
 public: