[TaskScheduler]: Migrate off of AssertBlockingAllowedDeprecated in /media/capture/video

base::AssertBlockingAllowedDeprecated is deprecated in favor of
ScopedBlockingCall, which serves as a precise annotation of
the scope that may/will block.

Please make sure of the following:
  - ScopedBlockingCall is instantiated in a scope with minimal CPU usage.
    If this is not the case, ScopedBlockingCall should be instantiated
    closer to the blocking call. See scoped_blocking_call.h for more
    info. Please let me know when/where the blocking call happens if this needs
    to be changed.
  - Parameter |blocking_type| matches expectation:
      MAY_BLOCK: The call might block (e.g. file I/O that might hit in memory cache).
      WILL_BLOCK: The call will definitely block (e.g. cache already checked and now pinging
        server synchronously).
    See BlockingType for more info. While I assumed MAY_BLOCK by default, that might
    not be the best fit if we know that this callsite is guaranteed to block.
  - The ScopedBlockingCall's scope covers the entirety of the blocking operation
    previously asserted against by the AssertBlockingAllowed().
  - Calls to blocking //base APIs don't need to be annotated
    with ScopedBlockingCall. All blocking //base APIs (e.g. base::ReadFileToString, base::File::Read,
    base::SysInfo::AmountOfFreeDiskSpace, base::WaitableEvent::Wait, etc.) have their
    own internal annotations.

Refer to the top-level CL if necessary :
https://chromium-review.googlesource.com/c/chromium/src/+/1338391

Please CQ if LGTY!

This CL was uploaded by git cl split.

R=emircan@chromium.org

Bug: 903957
Change-Id: Icb47a6a89a0c8e3c1a2871064dbb5b105db0ba2f
Reviewed-on: https://chromium-review.googlesource.com/c/1338412Reviewed-by: Emircan Uysaler <emircan@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608842}

media/capture/video/file_video_capture_device_factory.cc

@@ -7,7 +7,7 @@
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/strings/sys_string_conversions.h"
-#include "base/threading/thread_restrictions.h"
+#include "base/threading/scoped_blocking_call.h"
 #include "build/build_config.h"
 #include "media/base/media_switches.h"
 #include "media/capture/video/file_video_capture_device.h"
@@ -29,7 +29,7 @@ base::FilePath GetFilePathFromCommandLine() {
 std::unique_ptr<VideoCaptureDevice> FileVideoCaptureDeviceFactory::CreateDevice(
     const VideoCaptureDeviceDescriptor& device_descriptor) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  base::AssertBlockingAllowedDeprecated();
+  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::MAY_BLOCK);
 #if defined(OS_WIN)
   return std::unique_ptr<VideoCaptureDevice>(new FileVideoCaptureDevice(
       base::FilePath(base::SysUTF8ToWide(device_descriptor.display_name()))));
@@ -67,7 +67,7 @@ void FileVideoCaptureDeviceFactory::GetSupportedFormats(
     const VideoCaptureDeviceDescriptor& device_descriptor,
     VideoCaptureFormats* supported_formats) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  base::AssertBlockingAllowedDeprecated();
+  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::MAY_BLOCK);
 
   VideoCaptureFormat capture_format;
   if (!FileVideoCaptureDevice::GetVideoCaptureFormat(