DevTools: [HeapProfiler] Provide API for heap objects tracking info.

Source/devtools/protocol.json

 {
     "version": { "major": "1", "minor": "0" },
     "domains": [{
         "domain": "Inspector",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable",
                 "description": "Enables inspector domain notifications."
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             }
         ],
         "commands": [
             {
                 "name": "getProfileHeaders",
                 "returns": [
                     { "name": "headers", "type": "array", "items": { "$ref": "ProfileHeader"} }
                 ]
             },
             {
+                "name": "startTrackingHeapObjects"
+            },
+            {
+                "name": "stopTrackingHeapObjects"
+            },
+            {
                 "name": "getHeapSnapshot",
                 "parameters": [
                     { "name": "uid", "type": "integer" }
                 ]
             },
             {
                 "name": "removeProfile",
                 "parameters": [
                     { "name": "uid", "type": "integer" }
                 ]
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             },
             {
                 "name": "resetProfiles"
             },
             {
                 "name": "reportHeapSnapshotProgress",
                 "parameters": [
                     { "name": "done", "type": "integer" },
                     { "name": "total", "type": "integer" }
                 ]
+            },
+            {
+                "name": "lastSeenObjectId",
+                "description": "If heap objects tracking has been started then backend regulary sends a current value for last seen object id and corresponding timestamp. If the were changes in the heap since last event then one or more heapStatsUpdate events will be sent before a new lastSeenObjectId event.",
+                "parameters": [
+                    { "name": "lastSeenObjectId", "type": "integer" },
+                    { "name": "timestamp", "type": "number" }
+                ]
+            },
+            {
+                "name": "heapStatsUpdate",
+                "description": "If heap objects tracking has been started then backend may send update for one or more fragments",
+                "parameters": [
+                    { "name": "statsUpdate", "type": "array", "items": { "type": "integer" }, "description": "An array of triplets. Each triplet describes a fragment. The first integer is the fragment index, the second integer is a total count of objects for the fragment, the third integer is a total size of the objects for the fragment."}
+                ]
             }
         ]
     },
     {
         "domain": "Worker",
         "hidden": true,
         "types": [],
         "commands": [
             {
                 "name": "enable"
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                 ]
             }
         ],
         "events": [
             {
                 "name": "layerTreeDidChange"
             }
         ]
     }]
 }