ImageCapture: ScopedResultCallback

content/browser/media/capture/image_capture_impl.cc

Index: content/browser/media/capture/image_capture_impl.cc
diff --git a/content/browser/media/capture/image_capture_impl.cc b/content/browser/media/capture/image_capture_impl.cc
index 7a22bc9f7f59f72a340475d53aea6245003a6f5b..ee238a5d2b7dfbcf9e008d9fff4ed3e5fcdb2c0c 100644
--- a/content/browser/media/capture/image_capture_impl.cc
+++ b/content/browser/media/capture/image_capture_impl.cc
@@ -10,43 +10,56 @@
 #include "content/browser/renderer_host/media/video_capture_manager.h"
 #include "content/common/media/media_stream_options.h"
 #include "content/public/browser/browser_thread.h"
+#include "media/base/bind_to_current_loop.h"
 #include "media/capture/video/video_capture_device.h"
 
 namespace content {
 
 namespace {
 
-void RunMojoCallback(const ImageCaptureImpl::TakePhotoCallback& callback,
-                     const std::string& mime_type,
-                     mojo::Array<uint8_t> data) {
+void RunFailedGetCapabilitiesCallback(
+    const ImageCaptureImpl::GetCapabilitiesCallback& cb) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  blink::mojom::PhotoCapabilitiesPtr empty_capabilities =
+      blink::mojom::PhotoCapabilities::New();
+  empty_capabilities->zoom = blink::mojom::Range::New();
+  cb.Run(std::move(empty_capabilities));
+}
+
+void RunTakePhotoCallbackOnUIThread(
+    const ImageCaptureImpl::TakePhotoCallback& callback,
+    mojo::String mime_type,
+    mojo::Array<uint8_t> data) {
+  if (!BrowserThread::CurrentlyOn(BrowserThread::UI)) {

[miu, 2016/05/27 22:36:38]

Instead of trampolining, can you just use media::BindToCurrentLoop() on L91
below?

[mcasas, 2016/05/27 23:36:06]

media::BindToCurrentLoop() does not know how 
to forward mojo::Array<> etc, so until that time
comes, can't do that here -- unlike the other
RunFailed...Callback() functions, which do use it.

Actually, on second thoughts this function would 
never be called on UI thread since we already have
at least one jump to IO. So I simplified it a bit.

+    BrowserThread::PostTask(
+        BrowserThread::UI, FROM_HERE,
+        base::Bind(&RunTakePhotoCallbackOnUIThread, std::move(callback),
+                   mime_type, base::Passed(std::move(data))));
+    return;
+  }
+
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
   callback.Run(mime_type, std::move(data));
 }
 
-void RunTakePhotoCallback(const ImageCaptureImpl::TakePhotoCallback& callback,
-                          const std::string& mime_type,
-                          std::unique_ptr<std::vector<uint8_t>> data) {
-  DCHECK(data.get());
-  BrowserThread::PostTask(
-      BrowserThread::UI, FROM_HERE,
-      base::Bind(&RunMojoCallback, callback, mime_type,
-                 base::Passed(mojo::Array<uint8_t>::From(*data))));
+void RunFailedTakePhotoCallback(const ImageCaptureImpl::TakePhotoCallback& cb) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  cb.Run("", mojo::Array<uint8_t>());
 }
 
-void TakePhotoOnIOThread(const mojo::String& source_id,
-                         const ImageCaptureImpl::TakePhotoCallback& callback,
-                         MediaStreamManager* media_stream_manager) {
+void TakePhotoOnIOThread(
+    const mojo::String& source_id,
+    MediaStreamManager* media_stream_manager,
+    media::ScopedCallback<ImageCaptureImpl::TakePhotoCallback> callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   const int session_id =
       media_stream_manager->VideoDeviceIdToSessionId(source_id);
 
-  if (session_id == StreamDeviceInfo::kNoId ||
-      !media_stream_manager->video_capture_manager()->TakePhoto(
-          session_id, base::Bind(&RunTakePhotoCallback, callback))) {
-    std::unique_ptr<std::vector<uint8_t>> empty_vector(
-        new std::vector<uint8_t>());
-    RunTakePhotoCallback(callback, "", std::move(empty_vector));
-  }
+  if (session_id == StreamDeviceInfo::kNoId)
+    return;
+  media_stream_manager->video_capture_manager()->TakePhoto(session_id,
+                                                           std::move(callback));
 }
 
 }  // anonymous namespace
@@ -65,21 +78,25 @@ void ImageCaptureImpl::GetCapabilities(
     const GetCapabilitiesCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  blink::mojom::PhotoCapabilitiesPtr empty_capabilities =
-      blink::mojom::PhotoCapabilities::New();
-  empty_capabilities->zoom = blink::mojom::Range::New();
-  callback.Run(std::move(empty_capabilities));
+  media::ScopedCallback<GetCapabilitiesCallback> scoped_callback(
+      callback,
+      media::BindToCurrentLoop(base::Bind(&RunFailedGetCapabilitiesCallback)));
 }
 
-
 void ImageCaptureImpl::TakePhoto(const mojo::String& source_id,
                                  const TakePhotoCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  media::ScopedCallback<TakePhotoCallback> scoped_callback(
+      base::Bind(&RunTakePhotoCallbackOnUIThread, callback),
+      media::BindToCurrentLoop(base::Bind(&RunFailedTakePhotoCallback)));
+
   // media_stream_manager() can only be called on UI thread.
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
-      base::Bind(&TakePhotoOnIOThread, source_id, callback,
-                 BrowserMainLoop::GetInstance()->media_stream_manager()));
+      base::Bind(&TakePhotoOnIOThread, source_id,
+                 BrowserMainLoop::GetInstance()->media_stream_manager(),
+                 base::Passed(&scoped_callback)));
 }
 
 ImageCaptureImpl::ImageCaptureImpl(