Remove the MessageLoop::DestructionObserver from mojo bindings.

mojo/android/system/watcher_impl.cc

Index: mojo/android/system/watcher_impl.cc
diff --git a/mojo/android/system/watcher_impl.cc b/mojo/android/system/watcher_impl.cc
index 2a6c54cf4b5dd60b83a70899bc0b230da4bf5d96..756ffe3f3bcaf317cf0b72f7b8c9dc9c6366a7ec 100644
--- a/mojo/android/system/watcher_impl.cc
+++ b/mojo/android/system/watcher_impl.cc
@@ -13,7 +13,6 @@
 #include "base/android/library_loader/library_loader_hooks.h"
 #include "base/android/scoped_java_ref.h"
 #include "base/bind.h"
-#include "base/message_loop/message_loop.h"
 #include "jni/WatcherImpl_jni.h"
 #include "mojo/public/cpp/system/handle.h"
 #include "mojo/public/cpp/system/watcher.h"
@@ -25,41 +24,32 @@ using base::android::JavaParamRef;
 
 namespace {
 
-class WatcherWithMessageLoopObserver
-    : public base::MessageLoop::DestructionObserver {
+class WatcherImpl {
  public:
-  WatcherWithMessageLoopObserver() : watcher_(FROM_HERE) {}
+  WatcherImpl() : watcher_(FROM_HERE) {}
 
-  ~WatcherWithMessageLoopObserver() override { StopObservingIfNecessary(); }
+  ~WatcherImpl() = default;
 
   jint Start(JNIEnv* env,
              const JavaParamRef<jobject>& jcaller,
              jint mojo_handle,
              jint signals) {
-    if (!is_observing_) {
-      is_observing_ = true;
-      base::MessageLoop::current()->AddDestructionObserver(this);
-    }
-
     java_watcher_.Reset(env, jcaller);
 
-    auto ready_callback = base::Bind(
-        &WatcherWithMessageLoopObserver::OnHandleReady, base::Unretained(this));
+    auto ready_callback =
+        base::Bind(&WatcherImpl::OnHandleReady, base::Unretained(this));
 
     MojoResult result =
         watcher_.Start(mojo::Handle(static_cast<MojoHandle>(mojo_handle)),
                        static_cast<MojoHandleSignals>(signals), ready_callback);
 
-    if (result != MOJO_RESULT_OK) {
-      StopObservingIfNecessary();
+    if (result != MOJO_RESULT_OK)
       java_watcher_.Reset();
-    }
 
     return result;
   }
 
   void Cancel() {
-    StopObservingIfNecessary();
     java_watcher_.Reset();
     watcher_.Cancel();
   }
@@ -69,10 +59,8 @@ class WatcherWithMessageLoopObserver
     DCHECK(!java_watcher_.is_null());
 
     base::android::ScopedJavaGlobalRef<jobject> java_watcher_preserver;
-    if (result == MOJO_RESULT_CANCELLED) {
-      StopObservingIfNecessary();
+    if (result == MOJO_RESULT_CANCELLED)
       java_watcher_preserver = std::move(java_watcher_);
-    }
 
     Java_WatcherImpl_onHandleReady(
         base::android::AttachCurrentThread(),
@@ -80,30 +68,16 @@ class WatcherWithMessageLoopObserver
         result);
   }
 
-  // base::MessageLoop::DestructionObserver:
-  void WillDestroyCurrentMessageLoop() override {
-    StopObservingIfNecessary();
-    OnHandleReady(MOJO_RESULT_ABORTED);
-  }
-
-  void StopObservingIfNecessary() {
-    if (is_observing_) {
-      is_observing_ = false;
-      base::MessageLoop::current()->RemoveDestructionObserver(this);
-    }
-  }
-
-  bool is_observing_ = false;
   Watcher watcher_;
   base::android::ScopedJavaGlobalRef<jobject> java_watcher_;
 
-  DISALLOW_COPY_AND_ASSIGN(WatcherWithMessageLoopObserver);
+  DISALLOW_COPY_AND_ASSIGN(WatcherImpl);
 };
 
 }  // namespace
 
 static jlong CreateWatcher(JNIEnv* env, const JavaParamRef<jobject>& jcaller) {
-  return reinterpret_cast<jlong>(new WatcherWithMessageLoopObserver);
+  return reinterpret_cast<jlong>(new WatcherImpl);
 }
 
 static jint Start(JNIEnv* env,
@@ -111,20 +85,20 @@ static jint Start(JNIEnv* env,
                   jlong watcher_ptr,
                   jint mojo_handle,
                   jint signals) {
-  auto watcher = reinterpret_cast<WatcherWithMessageLoopObserver*>(watcher_ptr);
+  auto watcher = reinterpret_cast<WatcherImpl*>(watcher_ptr);
   return watcher->Start(env, jcaller, mojo_handle, signals);
 }
 
 static void Cancel(JNIEnv* env,
                    const JavaParamRef<jobject>& jcaller,
                    jlong watcher_ptr) {
-  reinterpret_cast<WatcherWithMessageLoopObserver*>(watcher_ptr)->Cancel();
+  reinterpret_cast<WatcherImpl*>(watcher_ptr)->Cancel();
 }
 
 static void Delete(JNIEnv* env,
                    const JavaParamRef<jobject>& jcaller,
                    jlong watcher_ptr) {
-  delete reinterpret_cast<WatcherWithMessageLoopObserver*>(watcher_ptr);
+  delete reinterpret_cast<WatcherImpl*>(watcher_ptr);
 }
 
 bool RegisterWatcherImpl(JNIEnv* env) {