[debug] [reland] Consistently use script from FrameMirror

src/inspector/debugger-script.js

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 475 matching lines @@
                 var scopeObject = DebuggerScript._buildScopeObject(scopeTypes[i], scopeObjects[i]);
                 if (scopeObject) {
                     scopeTypes[j] = scopeTypes[i];
                     scopeNames[j] = scopeNames[i];
                     scopeChain[j] = scopeObject;
 
                     var funcMirror = scopeFunctions ? MakeMirror(scopeFunctions[i]) : null;
                     if (!funcMirror || !funcMirror.isFunction())
                         funcMirror = new UnresolvedFunctionMirror(funcObject);
 
                     var script = /** @type {!FunctionMirror} */(funcMirror).script();

[kozy, 2016/10/13 16:06:18]

Does WASM frame contain scope chain? If yes, then should we use
frameMirror.script() here too?

[Clemens Hammacher, 2016/10/14 10:22:50]

No, there is no scope chain for WASM frames.
Also, I think the point of this code is to have different functions in the scope
chain, thus we also need to select the correct script per scope.

                     scopeStartLocations[j] = createLocation(script, scopeStartPositions[i]);
                     scopeEndLocations[j] = createLocation(script, scopeEndPositions[i]);
                     ++j;
                 }
             }
             scopeTypes.length = scopeChain.length;
             scopeNames.length = scopeChain.length;
             scopeObjects = null; // Free for GC.
             scopeFunctions = null;
             scopeStartPositions = null;
             scopeEndPositions = null;
         }
         return scopeChain;
     }
 
     /**
      * @return {!JavaScriptCallFrameDetails}
      */
     function lazyDetails()
     {
         if (!details) {
             var scopeObjects = ensureScopeChain();
-            var script = ensureFuncMirror().script();
+            var script = frameMirror.script();

[kozy, 2016/10/13 16:06:18]

Please store scriptMirror at the beginning of this function and then use it.
Using frameMirror in lazyDetails function can be dangerous since it can be
called not on pause. I think it's a root of crash in layout tests on blink bot.

[Clemens Hammacher, 2016/10/14 10:22:50]

Done. I also removed two checks for the existence of a script, since we now
always have a Script available (I double-checked this in runtime-debug.cc).

             /** @type {!Array<Scope>} */
             var scopes = [];
             for (var i = 0; i < scopeObjects.length; ++i) {
                 var scope = {
                     "type": /** @type {string} */(DebuggerScript._scopeTypeNames.get(scopeTypes[i])),
                     "object": scopeObjects[i],
                 };
                 if (scopeNames[i])
                     scope.name = scopeNames[i];
                 if (scopeStartLocations[i])
@@ skipping 38 matching lines @@
         }
         return /** @type {!FunctionMirror} */(funcMirror);
     }
 
     /**
      * @return {!{line: number, column: number}}
      */
     function ensureLocation()
     {
         if (!location) {
-            var script = ensureFuncMirror().script();
+            var script = frameMirror.script();
             if (script)
                 location = script.locationFromPosition(sourcePosition, true);
             if (!location)
                 location = { line: 0, column: 0 };
         }
         return location;
     }
 
     /**
      * @return {number}
@@ skipping 24 matching lines @@
         if (context)
             return DebuggerScript._executionContextId(context.data());
         return 0;
     }
 
     /**
      * @return {number|undefined}
      */
     function sourceID()
     {
-        var script = ensureFuncMirror().script();
+        var script = frameMirror.script();
         return script && script.id();
     }
 
     /**
      * @param {string} expression
      * @return {*}
      */
     function evaluate(expression)
     {
         return frameMirror.evaluate(expression, false).value();
@@ skipping 69 matching lines @@
         break;
     }
     return result;
 }
 
 // We never resolve Mirror by its handle so to avoid memory leaks caused by Mirrors in the cache we disable it.
 ToggleMirrorCache(false);
 
 return DebuggerScript;
 })();