Add 'NavigationHandle::QueueConsoleMessage'.

content/browser/frame_host/navigation_handle_impl.h

Index: content/browser/frame_host/navigation_handle_impl.h
diff --git a/content/browser/frame_host/navigation_handle_impl.h b/content/browser/frame_host/navigation_handle_impl.h
index b212b3ee7a7a0c3ac01fca8a1175370a26b99844..31251004c2d93bdfa11098b315dd413d79eb0b1a 100644
--- a/content/browser/frame_host/navigation_handle_impl.h
+++ b/content/browser/frame_host/navigation_handle_impl.h
@@ -18,6 +18,7 @@
 #include "content/common/content_export.h"
 #include "content/public/browser/navigation_data.h"
 #include "content/public/browser/navigation_throttle.h"
+#include "content/public/common/console_message_level.h"
 #include "url/gurl.h"
 
 struct FrameHostMsg_DidCommitProvisionalLoad_Params;
@@ -233,6 +234,13 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
     navigation_data_ = std::move(navigation_data);
   }
 
+  // Adds a console message to the NavigationHandle's message queue. Messages
+  // queued before the navigation is ready to commit will be delivered to the
+  // final RenderFrameHost upon commit. Messages queued after the navigation has
+  // committed will be delivered immediately.

[clamy, 2016/06/29 11:07:28]

The navigation commit corresponds to the destruction of this NavigationHandle,
so this comment seems a bit misleading to me. How about "at commit time" instead
of "after the navigation has committed".

There's also the question of what happens if the navigation doesn't commit.
Should we just drop them? Deliver them to the current RenderFrameHost of the
FrameTreeNode (maybe only if it was renderer initiated)? Once we come to an
agreement, this should be precised in the comment.

+  void QueueConsoleMessage(ConsoleMessageLevel level,

[nasko, 2016/06/28 22:25:46]

bikeshed: AppendConsoleMessage? Queue to me implies that it always adds to a
queue, which seems incorrect based on the description. Appending is always what
we want to do, regardless of whether we need to keep them in a queue for some
period of time.

+                           const std::string& message);
+
  private:
   friend class NavigationHandleImplTest;
 
@@ -267,6 +275,12 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
   // end of a round of NavigationThrottleChecks.
   void RunCompleteCallback(NavigationThrottle::ThrottleCheckResult result);
 
+  // Outputs the messages in |console_queue_| to the relevant RenderFrameHost,
+  // in FIFO order. This method must be called after a response has been
+  // delivered for processing, and will clear out |console_queue_| as a side
+  // effect of sending the messages.
+  virtual void DumpMessagesToConsole();

[clamy, 2016/06/29 11:07:28]

Why virtual?

+
   // Used in tests.
   State state() const { return state_; }
 
@@ -326,6 +340,9 @@ class CONTENT_EXPORT NavigationHandleImpl : public NavigationHandle {
   // Embedder data tied to this navigation.
   std::unique_ptr<NavigationData> navigation_data_;
 
+  // A queue of messages to be delivered to the devtools console upon commit.
+  std::queue<std::pair<ConsoleMessageLevel, const std::string>> console_queue_;
+
   DISALLOW_COPY_AND_ASSIGN(NavigationHandleImpl);
 };