Add a unique frame id and save it on HistoryItem.

Source/core/frame/Frame.cpp

Index: Source/core/frame/Frame.cpp
diff --git a/Source/core/frame/Frame.cpp b/Source/core/frame/Frame.cpp
index 1b7f0d1098515eec3985ea8f2b11d3ae18a2f1e3..b319fd0a283c1163e446b24b0351a261c5c51322 100644
--- a/Source/core/frame/Frame.cpp
+++ b/Source/core/frame/Frame.cpp
@@ -100,6 +100,12 @@ static inline float parentTextZoomFactor(Frame* frame)
     return parent->textZoomFactor();
 }
 
+static int64_t nextFrameID()
+{
+    static int64_t next = static_cast<long long>(currentTime() * 10000000);
+    return ++next;
+}
+
 inline Frame::Frame(Page* page, HTMLFrameOwnerElement* ownerElement, FrameLoaderClient* frameLoaderClient)
     : m_page(page)
     , m_treeNode(this, parentFromOwnerElement(ownerElement))
@@ -113,6 +119,7 @@ inline Frame::Frame(Page* page, HTMLFrameOwnerElement* ownerElement, FrameLoader
     , m_eventHandler(adoptPtr(new EventHandler(this)))
     , m_animationController(adoptPtr(new AnimationController(this)))
     , m_inputMethodController(InputMethodController::create(*this))
+    , m_id(nextFrameID())
     , m_pageZoomFactor(parentPageZoomFactor(this))
     , m_textZoomFactor(parentTextZoomFactor(this))
 #if ENABLE(ORIENTATION_EVENTS)