Fix DelegatedOutputSurface in Blimp

Make sure to build a BeginFrameSource when binding to the
OutputSurfaceClient.  Without this the compositor doesn't push frames.

This was broken by https://codereview.chromium.org/2083423006 because
BlimpLayerTreeSettings sets use_output_surface_begin_frame_source but
one wasn't provided by the DelegatedOutputSurface.

Infrastructure to add a Blimp test for this is almost complete and will
be added in a follow up CL!
BUG=

Review-Url: https://codereview.chromium.org/2308143002
Cr-Commit-Position: refs/heads/master@{#416395}

blimp/client/core/compositor/delegated_output_surface.cc

@@ -9,7 +9,11 @@
 #include "base/memory/ptr_util.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_checker.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "cc/output/compositor_frame.h"
+#include "cc/output/output_surface_client.h"
+#include "cc/scheduler/begin_frame_source.h"
+#include "cc/scheduler/delay_based_time_source.h"
 
 namespace blimp {
 namespace client {
@@ -46,6 +50,11 @@ uint32_t DelegatedOutputSurface::GetFramebufferCopyTextureFormat() {
 bool DelegatedOutputSurface::BindToClient(cc::OutputSurfaceClient* client) {
   bool success = cc::OutputSurface::BindToClient(client);
   if (success) {
+    begin_frame_source_ = base::MakeUnique<cc::DelayBasedBeginFrameSource>(
+        base::MakeUnique<cc::DelayBasedTimeSource>(
+            base::ThreadTaskRunnerHandle::Get().get()));
+    client->SetBeginFrameSource(begin_frame_source_.get());
+
     main_task_runner_->PostTask(
         FROM_HERE, base::Bind(&BlimpOutputSurfaceClient::BindToOutputSurface,
                               client_, weak_factory_.GetWeakPtr()));

blimp/client/core/compositor/delegated_output_surface.h

@@ -5,6 +5,8 @@
 #ifndef BLIMP_CLIENT_CORE_COMPOSITOR_DELEGATED_OUTPUT_SURFACE_H_
 #define BLIMP_CLIENT_CORE_COMPOSITOR_DELEGATED_OUTPUT_SURFACE_H_
 
+#include <memory>
+
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "blimp/client/core/compositor/blimp_output_surface.h"
@@ -15,6 +17,7 @@ class SingleThreadTaskRunner;
 }  // namespace base
 
 namespace cc {
+class BeginFrameSource;
 class ContextProvider;
 }  // namespace cc
 
@@ -50,6 +53,11 @@ class DelegatedOutputSurface : public cc::OutputSurface,
 
   bool bound_to_client_;
 
+  // This OutputSurface is responsible for providing the BeginFrameSource to
+  // drive frame creation.  This will be built on the compositor impl thread at
+  // BindToClient call time.
+  std::unique_ptr<cc::BeginFrameSource> begin_frame_source_;
+
   base::WeakPtrFactory<DelegatedOutputSurface> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DelegatedOutputSurface);

blimp/client/support/compositor/blimp_layer_tree_settings.cc

@@ -87,10 +87,6 @@ void PopulateCommonLayerTreeSettings(cc::LayerTreeSettings* settings) {
   // TODO(danakj): Only do this on low end devices.
   settings->create_low_res_tiling = true;
 
-// TODO(dtrainor): Investigate whether or not we want to use an external
-// source here.
-// settings->use_external_begin_frame_source = true;
-
 #elif !defined(OS_MACOSX)
   settings->scrollbar_animator = cc::LayerTreeSettings::LINEAR_FADE;
   settings->solid_color_scrollbar_color = SkColorSetARGB(128, 128, 128, 128);