[DevTools] allow nested command processing

It allows to break infinite loops started using Runtime.evaluate, e.g.
from console.

R=dgozman@chromium.org

Bug: chromium:820258
Change-Id: I9110ba6db50b60b803b2ec50291d31b854e216bf
Reviewed-on: https://chromium-review.googlesource.com/956525Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542014}

third_party/WebKit/LayoutTests/http/tests/devtools/sources/debugger-pause/debugger-pause-infinite-loop-expected.txt

+Tests that we can break infinite loop started from console.
+Run infinite loop
+Request pause
+Script execution paused.
+Change condition on pause to finish infinite loop
+Message count: 3
+Script execution resumed.
+Message count: 4
+while(a) {}; 42
+a = false
+false
+42
+Infinite loop finished
+

third_party/WebKit/LayoutTests/http/tests/devtools/sources/debugger-pause/debugger-pause-infinite-loop.js

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+(async function() {
+  TestRunner.addResult(
+      `Tests that we can break infinite loop started from console.`);
+  await TestRunner.loadModule('console_test_runner');
+  await TestRunner.loadModule('sources_test_runner');
+  await TestRunner.showPanel('sources');
+  await TestRunner.evaluateInPagePromise('a = true');
+
+  await SourcesTestRunner.startDebuggerTestPromise();
+  TestRunner.addResult('Run infinite loop');
+  ConsoleTestRunner.evaluateInConsole(`while(a) {}; 42`);
+  TestRunner.addResult('Request pause');
+  SourcesTestRunner.togglePause();
+  await SourcesTestRunner.waitUntilPausedPromise();
+  TestRunner.addResult('Change condition on pause to finish infinite loop');
+  ConsoleTestRunner.evaluateInConsole('a = false');
+  await ConsoleTestRunner.waitForConsoleMessagesPromise(3);
+  await new Promise(resolve => SourcesTestRunner.resumeExecution(resolve));
+  await ConsoleTestRunner.waitForConsoleMessagesPromise(4);
+  ConsoleTestRunner.dumpConsoleMessages();
+  TestRunner.addResult('Infinite loop finished');
+  SourcesTestRunner.completeDebuggerTest();
+})();

third_party/WebKit/Source/core/exported/WebDevToolsAgentImpl.cpp

@@ -385,8 +385,6 @@ void WebDevToolsAgentImpl::Session::DispatchProtocolCommand(
   // detach, so we have to check a flag here.
   if (detached_)
     return;
-  InspectorTaskRunner::IgnoreInterruptsScope scope(
-      frame_->GetFrame()->GetInspectorTaskRunner());
   inspector_session_->DispatchProtocolMessage(method, message);
 }