Not for review - Rebase of crrev.com/62833003

Source/platform/UIWebThreadSupportingGC.h

Index: Source/platform/UIWebThreadSupportingGC.h
diff --git a/Source/platform/UIWebThreadSupportingGC.h b/Source/platform/UIWebThreadSupportingGC.h
new file mode 100644
index 0000000000000000000000000000000000000000..925a9a01a5ffe9248b235fcde7286b2f09aa8b4c
--- /dev/null
+++ b/Source/platform/UIWebThreadSupportingGC.h
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+#ifndef UIWEBTHREADSUPPORTINGGC
+#define UIWEBTHREADSUPPORTINGGC
+
+#include "WebThreadSupportingGC.h"
+#include "wtf/HashMap.h"
+
+namespace blink {
+
+class PLATFORM_EXPORT UIWebThreadSupportingGC : public WebThreadSupportingGC {
+    WTF_MAKE_NONCOPYABLE(UIWebThreadSupportingGC);
+  public:
+    static PassOwnPtr<UIWebThreadSupportingGC> create(const char* name);
+    static UIWebThreadSupportingGC* get(WebThread* t);
+
+    virtual void attachGC() override;
+    virtual void detachGC() override;
+
+  private:
+    // should never create 2 UIWebThreadSupportingGCs pointing to the same thread
+    UIWebThreadSupportingGC(const char* name);
+    UIWebThreadSupportingGC(WebThread* t);
+
+    typedef HashMap<WebThread*, UIWebThreadSupportingGC*> ThreadMap;
+    static ThreadMap* m_threadMap;
+
+    int m_attachedThreads;
+};
+
+}
+
+#endif /* ifndef UIWEBTHREADSUPPORTINGGC */