Support performance.now() in workers.

Source/modules/performance/WorkerPerformance.cpp

Index: Source/modules/performance/WorkerPerformance.cpp
diff --git a/Source/core/html/ime/Composition.cpp b/Source/modules/performance/WorkerPerformance.cpp
similarity index 79%
copy from Source/core/html/ime/Composition.cpp
copy to Source/modules/performance/WorkerPerformance.cpp
index e74501bcd8637afa85872dae701e91f04827e1ee..cd39e13ff2537529d167ec9ab7ff2408b1bc14ed 100644
--- a/Source/core/html/ime/Composition.cpp
+++ b/Source/modules/performance/WorkerPerformance.cpp
@@ -29,27 +29,26 @@
  */
 
 #include "config.h"
-#include "core/html/ime/Composition.h"
+#include "modules/performance/WorkerPerformance.h"
 
-#include "core/dom/Node.h"
-#include "core/dom/Range.h"
+#include "core/workers/DedicatedWorkerContext.h"
+#include "core/workers/WorkerContext.h"
+#include "wtf/CurrentTime.h"
 
 namespace WebCore {
 
-Composition::~Composition()
+WorkerPerformance::WorkerPerformance(WorkerContext* context)
+    : m_context(context)
 {
 }
 
-PassRefPtr<Composition> Composition::create(Node* text, Range* caret)
+WorkerPerformance::~WorkerPerformance()
 {
-    return adoptRef(new Composition(text, caret));
 }
 
-Composition::Composition(Node* text, Range* caret)
-    : m_text(text)
-    , m_caret(caret)
+double WorkerPerformance::now() const
 {
-    ScriptWrappable::init(this);
+    return 1000.0 * (monotonicallyIncreasingTime() - m_context->timeOrigin());
 }
 
 } // namespace WebCore