[debug] change coverage API to use offset instead of line/column.

src/inspector/js_protocol.json

 {
     "version": { "major": "1", "minor": "2" },
     "domains": [
     {
         "domain": "Schema",
         "description": "Provides information about the protocol schema.",
         "types": [
             {
                 "id": "Domain",
                 "type": "object",
@@ skipping 834 matching lines @@
                 ]
             },
             {   "id": "CoverageRange",
                 "type": "object",
                 "description": "Coverage data for a source range.",
                 "properties": [
                     { "name": "startLineNumber", "type": "integer", "description": "JavaScript script line number (0-based) for the range start." },
                     { "name": "startColumnNumber", "type": "integer", "description": "JavaScript script column number (0-based) for the range start." },
                     { "name": "endLineNumber", "type": "integer", "description": "JavaScript script line number (0-based) for the range end." },
                     { "name": "endColumnNumber", "type": "integer", "description": "JavaScript script column number (0-based) for the range end." },
+                    { "name": "startOffset", "type": "integer", "description": "JavaScript script source offset for the range start." },
+                    { "name": "endOffset", "type": "integer", "description": "JavaScript script source offset for the range end." },
                     { "name": "count", "type": "integer", "description": "Collected execution count of the source range." }
                 ],
                 "experimental": true
             },
             {   "id": "FunctionCoverage",
                 "type": "object",
                 "description": "Coverage data for a JavaScript function.",
                 "properties": [
                     { "name": "functionName", "type": "string", "description": "JavaScript function name." },
                     { "name": "ranges", "type": "array", "items": { "$ref": "CoverageRange" }, "description": "Source ranges inside the function with coverage data." }
@@ skipping 208 matching lines @@
             {
                 "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."}
                 ]
             }
         ]
     }]
 }