[TaskScheduler]: Use ScopedBlockingCall to mark blocking tasks.

This CL uses ScopedBlockingCall to mark blocking calls in /ios/chrome/browser/ui.

This CL was created by replacing calls to AssertBlockingAllowed()
with instantiations of ScopedBlockingCall(MAY_BLOCK).
I kindly ask the reviewer to 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/WILL_BLOCK). 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().

This CL was uploaded by git cl split.

R=marq@chromium.org

Bug: 874080
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: I519b492dc31621ebc2f85fb7952a48e286e21d9f
Reviewed-on: https://chromium-review.googlesource.com/1191532Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587550}

ios/chrome/browser/ui/external_file_controller.mm

@@ -8,7 +8,7 @@
 
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
-#include "base/threading/thread_restrictions.h"
+#include "base/threading/scoped_blocking_call.h"
 #import "ios/chrome/browser/tabs/tab_model.h"
 #import "ios/web/public/web_view_creation_util.h"
 
@@ -80,7 +80,7 @@ const CFTimeInterval kSecondsPerDay = 60 * 60 * 24;
 
 + (void)removeFilesExcluding:(NSSet*)filesToKeep
                    olderThan:(NSInteger)ageInDays {
-  base::AssertBlockingAllowed();
+  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::WILL_BLOCK);
   NSFileManager* fileManager = [NSFileManager defaultManager];
   NSString* inboxDirectory = [ExternalFileController inboxDirectoryPath];
   NSArray* externalFiles =

ios/chrome/browser/ui/open_in_controller.mm

@@ -12,7 +12,7 @@
 
 #include "base/sequenced_task_runner.h"
 #include "base/strings/sys_string_conversions.h"
-#include "base/threading/thread_restrictions.h"
+#include "base/threading/scoped_blocking_call.h"
 #include "components/strings/grit/components_strings.h"
 #import "ios/chrome/browser/ui/alert_coordinator/alert_coordinator.h"
 #import "ios/chrome/browser/ui/open_in_controller_testing.h"
@@ -510,7 +510,7 @@ class OpenInControllerBridge
 #pragma mark File management
 
 - (void)removeDocumentAtPath:(NSString*)path {
-  base::AssertBlockingAllowed();
+  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::WILL_BLOCK);
   NSFileManager* fileManager = [NSFileManager defaultManager];
   NSError* error = nil;
   if (![fileManager removeItemAtPath:path error:&error]) {
@@ -520,7 +520,7 @@ class OpenInControllerBridge
 }
 
 + (void)removeAllStoredDocumentsAtPath:(NSString*)tempDirPath {
-  base::AssertBlockingAllowed();
+  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::WILL_BLOCK);
   NSFileManager* fileManager = [NSFileManager defaultManager];
   NSError* error = nil;
   NSArray* documentFiles =
@@ -541,7 +541,7 @@ class OpenInControllerBridge
 }
 
 + (BOOL)createDestinationDirectoryAndRemoveObsoleteFiles {
-  base::AssertBlockingAllowed();
+  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::WILL_BLOCK);
   NSString* tempDirPath = [NSTemporaryDirectory()
       stringByAppendingPathComponent:kDocumentsTempPath];
   NSFileManager* fileManager = [NSFileManager defaultManager];