arc: Notify ARC instance failures via callbacks.

components/arc/arc_bridge_bootstrap.h

Index: components/arc/arc_bridge_bootstrap.h
diff --git a/components/arc/arc_bridge_bootstrap.h b/components/arc/arc_bridge_bootstrap.h
index 918c2c0bba838a31e4fa36bc55ae9c825c10e2c5..91a4f6a1e28a9af49a13134fbdf83e202b4d72e1 100644
--- a/components/arc/arc_bridge_bootstrap.h
+++ b/components/arc/arc_bridge_bootstrap.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/sequenced_task_runner.h"
 #include "base/single_thread_task_runner.h"
+#include "components/arc/arc_bridge_service.h"
 #include "components/arc/common/arc_bridge.mojom.h"
 
 namespace arc {
@@ -19,10 +20,25 @@ namespace arc {
 // being available.
 class ArcBridgeBootstrap {
  public:
+  using AbortReason = ArcBridgeService::AbortReason;
+
   class Delegate {
    public:
+    // Called when a connection with ARC instance has been established.

[Luis Héctor Chávez, 2016/07/08 18:01:02]

nit: when the connection

[Shuhei Takahashi, 2016/07/11 08:25:19]

Done.

     virtual void OnConnectionEstablished(
         mojom::ArcBridgeInstancePtr instance_ptr) = 0;
+
+    // Called when ARC instance is being aborted due to errors.
+    // This can happen if it has failed to boot, or it has crashed after boot.
+    // After this callback is invoked, the ARC instance will be stopped, so
+    // you do not need to call ArcBridgeBootstrap::Stop() in the callback.
+    // Note: This callback can be called multiple times before OnStopped() if
+    // we encounter multiple errors during the process.
+    virtual void OnAborting(AbortReason reason) = 0;
+
+    // Called when ARC instance has stopped.
+    // When the ARC instance is being aborted due to errors, OnAborting() is
+    // called first, then OnStopped() is called once the instance is stopped.
     virtual void OnStopped() = 0;

[Luis Héctor Chávez, 2016/07/08 18:01:02]

Do you have an example of an instance where OnAborting() would need to be called
more than once before calling OnStopped()? Is there any way we can avoid that?

I think I'd prefer to have only OnStopped() with a StopReason parameter (where
it can be BOOT_FAILURE, CRASH, or CLEAN_TERMINATION). At least that way the
opt-in flow can have a slightly simpler implementation.

[Shuhei Takahashi, 2016/07/11 08:25:19]

It is possible ArcBridgeBootstrap encounters multiple errors. For example, both
ArcBridgeBootstrapImpl::AcceptInstanceConnection() failure and ARC container
crash can happen at the same time.

Anyway, I agree adding StopReason parameter to OnStopped() is easier to use from
callers. I've updated the patch to add a OnStopped()/OnBridgeStopped()
parameter, instead of adding a new observer method.

   };