Add observers to FrameSinkManagerHost.

content/browser/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//gpu/vulkan/features.gni")
 import("//media/media_options.gni")
 import("//ppapi/features/features.gni")
 import("//printing/features/features.gni")
@@ skipping 453 matching lines @@
     "cocoa/system_hotkey_helper_mac.h",
     "cocoa/system_hotkey_helper_mac.mm",
     "cocoa/system_hotkey_map.h",
     "cocoa/system_hotkey_map.mm",
 
     # NOTE: These files are here instead of in compositor_browser_sources
     # because the latter is not built on Android, whereas these files are
     # needed on all platforms.
     "compositor/frame_sink_manager_host.cc",
     "compositor/frame_sink_manager_host.h",
+    "compositor/frame_sink_observer.h",
     "compositor/surface_utils.cc",
     "compositor/surface_utils.h",
     "devtools/browser_devtools_agent_host.cc",
     "devtools/browser_devtools_agent_host.h",
     "devtools/devtools_agent_host_impl.cc",
     "devtools/devtools_agent_host_impl.h",
     "devtools/devtools_frame_trace_recorder.cc",
     "devtools/devtools_frame_trace_recorder.h",
     "devtools/devtools_http_handler.cc",
     "devtools/devtools_http_handler.h",
@@ skipping 1609 matching lines @@
   if (!is_component_build) {
     public_deps = [
       ":browser",
     ]
   } else {
     public_deps = [
       "//third_party/leveldatabase",
     ]
   }
 }