[TaskScheduler]: Use AssertLongCPUWorkAllowed to better match intent in chrome/browser/android

Instead of ScopedBlockingCall or AssertBlockingAllowed(),
AssertLongCPUWorkAllowed is used in FinalizeLauncherIconInBackground()
and in CreateLauncherIconFromFaviconInBackground().

Original CL intention was:
This CL uses ScopedBlockingCall to mark blocking calls in /chrome/browser/android/webapps.

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=dominickn@chromium.org

Bug: 874080
Change-Id: I31ed4164dbd93d424b7a3a69f833519d13c6fbf1
Reviewed-on: https://chromium-review.googlesource.com/1191185Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593708}

chrome/browser/android/shortcut_helper.cc

@@ -16,7 +16,7 @@
 #include "base/optional.h"
 #include "base/strings/string16.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/threading/scoped_blocking_call.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 #include "chrome/browser/android/color_helpers.h"
 #include "chrome/browser/android/webapk/chrome_webapk_host.h"
@@ -257,7 +257,7 @@ SkBitmap ShortcutHelper::FinalizeLauncherIconInBackground(
     const SkBitmap& bitmap,
     const GURL& url,
     bool* is_generated) {
-  base::ScopedBlockingCall scoped_blocking_call(base::BlockingType::MAY_BLOCK);
+  base::AssertLongCPUWorkAllowed();
 
   JNIEnv* env = base::android::AttachCurrentThread();
   ScopedJavaLocalRef<jobject> result;

chrome/browser/android/webapps/add_to_homescreen_data_fetcher.cc

@@ -11,6 +11,7 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/user_metrics.h"
 #include "base/task/post_task.h"
+#include "base/threading/thread_restrictions.h"
 #include "chrome/browser/android/shortcut_helper.h"
 #include "chrome/browser/android/webapk/chrome_webapk_host.h"
 #include "chrome/browser/android/webapk/webapk_web_manifest_checker.h"
@@ -67,8 +68,6 @@ InstallableParams ParamsToPerformInstallableCheck() {
 // - whether |icon| was used in generating the launcher icon
 std::pair<SkBitmap, bool> CreateLauncherIconInBackground(const GURL& start_url,
                                                          const SkBitmap& icon) {
-  base::AssertBlockingAllowed();
-
   bool is_generated = false;
   SkBitmap primary_icon = ShortcutHelper::FinalizeLauncherIconInBackground(
       icon, start_url, &is_generated);
@@ -84,10 +83,9 @@ std::pair<SkBitmap, bool> CreateLauncherIconInBackground(const GURL& start_url,
 std::pair<SkBitmap, bool> CreateLauncherIconFromFaviconInBackground(
     const GURL& start_url,
     const favicon_base::FaviconRawBitmapResult& bitmap_result) {
-  base::AssertBlockingAllowed();
-
   SkBitmap decoded;
   if (bitmap_result.is_valid()) {
+    base::AssertLongCPUWorkAllowed();
     gfx::PNGCodec::Decode(bitmap_result.bitmap_data->front(),
                           bitmap_result.bitmap_data->size(), &decoded);
   }