DevTools: Remove console last result $_ on console clear.

BUG=398336
R=loislo, yurys

Review URL: https://codereview.chromium.org/430503002

git-svn-id: svn://svn.chromium.org/blink/trunk@179179 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/inspector/console/console-eval-syntax-error-expected.txt

 Tests that evaluating an expression with a syntax error in the console won't crash the browser. Bug 61194.
 
 foo().
-Uncaught SyntaxError: Unexpected token } VM:734
+Uncaught SyntaxError: Unexpected token } VM:736
 

third_party/WebKit/LayoutTests/inspector/console/console-last-result-expected.txt

 Tests that console exposes last evaluation result as $_.
 
+
+Running: testLastResult
 1+1
 2
 $_
 2
 
+Running: testLastResultAfterConsoleClear
+$_
+undefined
+

third_party/WebKit/LayoutTests/inspector/console/console-last-result.html

@@ -6,17 +6,44 @@
 
 function test()
 {
-    InspectorTest.evaluateInConsole("1+1", step1);
+    InspectorTest.runTestSuite([
+        function testLastResult(next)
+        {
+            InspectorTest.evaluateInConsole("1+1", step1);
 
-    function step1()
-    {
-        InspectorTest.evaluateInConsole("$_", callback);
-    }
+            function step1()
+            {
+                evaluateLastResultAndDump(next);
+            }
+        },
+
+        function testLastResultAfterConsoleClear(next)
+        {
+            InspectorTest.evaluateInConsole("1+1", step1);
 
-    function callback()
+            function step1()
+            {
+                WebInspector.consoleModel.requestClearMessages();
+                InspectorTest.runAfterPendingDispatches(step2);
+            }
+
+            function step2()
+            {
+                evaluateLastResultAndDump(next);
+            }
+        }
+    ]);
+
+    function evaluateLastResultAndDump(callback)
     {
-        InspectorTest.dumpConsoleMessages();
-        InspectorTest.completeTest();
+        InspectorTest.evaluateInConsole("$_", didEvaluate);
+
+        function didEvaluate()
+        {
+            InspectorTest.dumpConsoleMessages();
+            if (callback)
+                callback();
+        }
     }
 }
 

third_party/WebKit/Source/core/inspector/InjectedScriptSource.js

@@ -359,6 +359,8 @@ InjectedScript.prototype = {
      */
     releaseObjectGroup: function(objectGroupName)
     {
+        if (objectGroupName === "console")
+            delete this._lastResult;
         var group = this._objectGroups[objectGroupName];
         if (!group)
             return;