DevTools: use per-LocalFrame instrumenting agents instead of per-Page ones.

Source/core/frame/LocalFrame.h

Index: Source/core/frame/LocalFrame.h
diff --git a/Source/core/frame/LocalFrame.h b/Source/core/frame/LocalFrame.h
index 8699d3fdb3cfa1c4f43ac30355798425fcb58573..0393d00ae1548847b43019ab159d2082cb0c0065 100644
--- a/Source/core/frame/LocalFrame.h
+++ b/Source/core/frame/LocalFrame.h
@@ -57,6 +57,7 @@ namespace blink {
     class InputMethodController;
     class IntPoint;
     class IntSize;
+    class InstrumentingAgents;
     class LocalDOMWindow;
     class Node;
     class Range;
@@ -125,6 +126,9 @@ namespace blink {
         // should be updated to avoid storing things on the main frame.
         LocalFrame* localFrameRoot();
 
+        InstrumentingAgents* instrumentingAgents();
+        void setInstrumentingAgents(InstrumentingAgents*);
+
     // ======== All public functions below this point are candidates to move out of LocalFrame into another class. ========
 
         bool inScope(TreeScope*) const;
@@ -222,6 +226,8 @@ namespace blink {
         float m_textZoomFactor;
 
         bool m_inViewSourceMode;
+
+        RefPtrWillBeMember<InstrumentingAgents> m_instrumentingAgents;
     };
 
     inline void LocalFrame::init()