[DevTools] Fix a race when inspecting shared/service worker

When pausing on initialization, we issue Debugger.enable
immediately followed by Debugger.pause and expect the pause to happen.

Because Debugger.pause can interrupt JS, it may actually run before
Debugger.enable on the backend. That makes pause noop, and we never
pause.

The solution is to await for Debugger.enable before asking to pause.

Bug: 775132, 900432
Change-Id: Ic2f504875b98312839235c6e32a10403757444f2
Reviewed-on: https://chromium-review.googlesource.com/c/1309213
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604299}

third_party/blink/renderer/devtools/front_end/sdk/ChildTargetManager.js

@@ -30,7 +30,7 @@ SDK.ChildTargetManager = class extends SDK.SDKModel {
   }
 
   /**
-   * @param {function({target: !SDK.Target, waitingForDebugger: boolean})=} attachCallback
+   * @param {function({target: !SDK.Target, waitingForDebugger: boolean}):!Promise=} attachCallback
    */
   static install(attachCallback) {
     SDK.ChildTargetManager._attachCallback = attachCallback;
@@ -138,9 +138,13 @@ SDK.ChildTargetManager = class extends SDK.SDKModel {
         targetInfo.targetId, targetName, this._capabilitiesForType(targetInfo.type),
         this._createChildConnection.bind(this, this._targetAgent, sessionId), this._parentTarget, false /* isNodeJS */);
 
-    if (SDK.ChildTargetManager._attachCallback)
-      SDK.ChildTargetManager._attachCallback({target, waitingForDebugger});
-    target.runtimeAgent().runIfWaitingForDebugger();
+    if (SDK.ChildTargetManager._attachCallback) {
+      SDK.ChildTargetManager._attachCallback({target, waitingForDebugger}).then(() => {
+        target.runtimeAgent().runIfWaitingForDebugger();
+      });
+    } else {
+      target.runtimeAgent().runIfWaitingForDebugger();
+    }
   }
 
   /**

third_party/blink/renderer/devtools/front_end/sdk/DebuggerModel.js

@@ -136,6 +136,14 @@ SDK.DebuggerModel = class extends SDK.SDKModel {
       return;
     SDK.DebuggerModel._debuggerIdToModel.set(debuggerId, this);
     this._debuggerId = debuggerId;
+    this.dispatchEventToListeners(SDK.DebuggerModel.Events.DebuggerIsReadyToPause, this);
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isReadyToPause() {
+    return !!this._debuggerId;
   }
 
   /**
@@ -929,7 +937,8 @@ SDK.DebuggerModel.Events = {
   DiscardedAnonymousScriptSource: Symbol('DiscardedAnonymousScriptSource'),
   GlobalObjectCleared: Symbol('GlobalObjectCleared'),
   CallFrameSelected: Symbol('CallFrameSelected'),
-  ConsoleCommandEvaluatedInSelectedCallFrame: Symbol('ConsoleCommandEvaluatedInSelectedCallFrame')
+  ConsoleCommandEvaluatedInSelectedCallFrame: Symbol('ConsoleCommandEvaluatedInSelectedCallFrame'),
+  DebuggerIsReadyToPause: Symbol('DebuggerIsReadyToPause'),
 };
 
 /** @enum {string} */

third_party/blink/renderer/devtools/front_end/worker_main/WorkerMain.js

@@ -27,12 +27,15 @@ WorkerMain.WorkerMain = class extends Common.Object {
   }
 };
 
-SDK.ChildTargetManager.install(({target, waitingForDebugger}) => {
+SDK.ChildTargetManager.install(async ({target, waitingForDebugger}) => {
   const parentTarget = target.parentTarget();
   // Only pause the new worker if debugging SW - we are going through the pause on start checkbox.
-  if (!parentTarget.parentTarget() && waitingForDebugger) {
-    const debuggerModel = target.model(SDK.DebuggerModel);
-    if (debuggerModel)
-      debuggerModel.pause();
-  }
+  if (parentTarget.parentTarget() || !waitingForDebugger)
+    return;
+  const debuggerModel = target.model(SDK.DebuggerModel);
+  if (!debuggerModel)
+    return;
+  if (!debuggerModel.isReadyToPause())
+    await debuggerModel.once(SDK.DebuggerModel.Events.DebuggerIsReadyToPause);
+  debuggerModel.pause();
 });