[inspector] extend protocol for code coverage.

test/inspector/runtime/coverage-expected.txt

+Test collecting code coverage data with Runtime.collectCoverage.
+
+Running test: testCoverage
+{
+    id : <messageId>
+    result : {
+        result : {
+            description : 8
+            type : number
+            value : 8
+        }
+    }
+}
+{
+    id : <messageId>
+    result : {
+        result : [
+            [0] : {
+                scriptId : <scriptId>
+                toplevel : {
+                    count : 1
+                    endColumnNumber : 0
+                    endLineNumber : 6
+                    functionName : 
+                    nested : [
+                        [0] : {
+                            count : 15
+                            endColumnNumber : 1
+                            endLineNumber : 4
+                            functionName : fib
+                            nested : [
+                            ]
+                            startColumnNumber : 0
+                            startLineNumber : 1
+                        }
+                    ]
+                    startColumnNumber : 0
+                    startLineNumber : 0
+                }
+                url : fib.js
+            }
+        ]
+    }
+}