[DevTools] Fix frontend host race and assert.

chrome/browser/devtools/devtools_ui_bindings.cc

Index: chrome/browser/devtools/devtools_ui_bindings.cc
diff --git a/chrome/browser/devtools/devtools_ui_bindings.cc b/chrome/browser/devtools/devtools_ui_bindings.cc
index acd7397bd037ed93d328383b7d014fea6ab04cda..f7ac4f9613a6904822ca0bcbf68d8c29c8fa778b 100644
--- a/chrome/browser/devtools/devtools_ui_bindings.cc
+++ b/chrome/browser/devtools/devtools_ui_bindings.cc
@@ -484,6 +484,7 @@ DevToolsUIBindings::DevToolsUIBindings(content::WebContents* web_contents)
       delegate_(new DefaultBindingsDelegate(web_contents_)),
       devices_updates_enabled_(false),
       frontend_loaded_(false),
+      frontend_reattaching_(false),
       weak_factory_(this) {
   g_instances.Get().push_back(this);
   frontend_contents_observer_.reset(new FrontendWebContentsObserver(this));
@@ -893,7 +894,7 @@ void DevToolsUIBindings::ClearPreferences() {
 
 void DevToolsUIBindings::DispatchProtocolMessageFromDevToolsFrontend(
     const std::string& message) {
-  if (agent_host_.get())
+  if (agent_host_.get() && !frontend_reattaching_)

[pfeldman, 2015/12/07 21:38:42]

When does this happen and why should it be ignored?

[dgozman, 2015/12/07 21:46:40]

Happens in Reattach. First paragraph of the patch description answers the second
question.

[pfeldman, 2015/12/07 21:48:36]

But how can it be dispatched twice?

[dgozman, 2015/12/07 22:03:53]

Sorry, it wasn't clear. It's not the same message dispatched twice, but one more
similar message. I've updated description.

     agent_host_->DispatchProtocolMessage(message);
 }
 
@@ -1126,6 +1127,7 @@ void DevToolsUIBindings::AttachTo(
 }
 
 void DevToolsUIBindings::Reattach() {
+  frontend_reattaching_ = true;
   DCHECK(agent_host_.get());
   agent_host_->DetachClient();
   agent_host_->AttachClient(this);
@@ -1175,6 +1177,7 @@ void DevToolsUIBindings::CallClientFunction(const std::string& function_name,
 }
 
 void DevToolsUIBindings::DocumentOnLoadCompletedInMainFrame() {
+  frontend_reattaching_ = false;
   // In the DEBUG_DEVTOOLS mode, the DocumentOnLoadCompletedInMainFrame event
   // arrives before the LoadCompleted event, thus it should not trigger the
   // frontend load handling.