Make USER_BLOCKING the default priority

We will then selectively downgrade tasks to USER_VISIBLE.

Eventually we want all task priorities to be either inherited or
explicitly set, so no defaults will be used. Roots will need to
explicitly set the priority (most likely USER_BLOCKING) thus that is a
good default for now.

Bug: 863341

Change-Id: I9872976bb944bc78dd43cbb6aff0cb5912043936
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1634702Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664726}

base/task/scoped_set_task_priority_for_current_thread.cc

@@ -34,7 +34,7 @@ ScopedSetTaskPriorityForCurrentThread::
 TaskPriority GetTaskPriorityForCurrentThread() {
   const TaskPriority* priority =
       tls_task_priority_for_current_thread.Get().Get();
-  return priority ? *priority : TaskPriority::USER_VISIBLE;
+  return priority ? *priority : TaskPriority::USER_BLOCKING;
 }
 
 }  // namespace internal

base/task/scoped_set_task_priority_for_current_thread_unittest.cc

@@ -12,14 +12,13 @@ namespace internal {
 
 TEST(ScopedSetTaskPriorityForCurrentThreadTest,
      ScopedSetTaskPriorityForCurrentThread) {
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, GetTaskPriorityForCurrentThread());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, GetTaskPriorityForCurrentThread());
   {
     ScopedSetTaskPriorityForCurrentThread
-        scoped_set_task_priority_for_current_thread(
-            TaskPriority::USER_BLOCKING);
-    EXPECT_EQ(TaskPriority::USER_BLOCKING, GetTaskPriorityForCurrentThread());
+        scoped_set_task_priority_for_current_thread(TaskPriority::BEST_EFFORT);
+    EXPECT_EQ(TaskPriority::BEST_EFFORT, GetTaskPriorityForCurrentThread());
   }
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, GetTaskPriorityForCurrentThread());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, GetTaskPriorityForCurrentThread());
 }
 
 }  // namespace internal

base/task/task_traits.h

@@ -195,7 +195,7 @@ class BASE_EXPORT TaskTraits {
             trait_helpers::AreValidTraits<ValidTrait, ArgTypes...>{},
             args...)),
         priority_(
-            trait_helpers::GetEnum<TaskPriority, TaskPriority::USER_VISIBLE>(
+            trait_helpers::GetEnum<TaskPriority, TaskPriority::USER_BLOCKING>(
                 args...)),
         shutdown_behavior_(
             trait_helpers::GetEnum<TaskShutdownBehavior,

base/task/task_traits_unittest.cc

@@ -11,7 +11,7 @@ namespace base {
 TEST(TaskTraitsTest, Default) {
   constexpr TaskTraits traits = {};
   EXPECT_FALSE(traits.priority_set_explicitly());
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, traits.priority());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, traits.priority());
   EXPECT_EQ(TaskShutdownBehavior::SKIP_ON_SHUTDOWN, traits.shutdown_behavior());
   EXPECT_EQ(ThreadPolicy::PREFER_BACKGROUND, traits.thread_policy());
   EXPECT_FALSE(traits.may_block());
@@ -31,7 +31,7 @@ TEST(TaskTraitsTest, TaskPriority) {
 TEST(TaskTraitsTest, TaskShutdownBehavior) {
   constexpr TaskTraits traits = {TaskShutdownBehavior::BLOCK_SHUTDOWN};
   EXPECT_FALSE(traits.priority_set_explicitly());
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, traits.priority());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, traits.priority());
   EXPECT_EQ(TaskShutdownBehavior::BLOCK_SHUTDOWN, traits.shutdown_behavior());
   EXPECT_EQ(ThreadPolicy::PREFER_BACKGROUND, traits.thread_policy());
   EXPECT_FALSE(traits.may_block());
@@ -41,7 +41,7 @@ TEST(TaskTraitsTest, TaskShutdownBehavior) {
 TEST(TaskTraitsTest, ThreadPolicy) {
   constexpr TaskTraits traits = {ThreadPolicy::MUST_USE_FOREGROUND};
   EXPECT_FALSE(traits.priority_set_explicitly());
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, traits.priority());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, traits.priority());
   EXPECT_EQ(TaskShutdownBehavior::SKIP_ON_SHUTDOWN, traits.shutdown_behavior());
   EXPECT_EQ(ThreadPolicy::MUST_USE_FOREGROUND, traits.thread_policy());
   EXPECT_FALSE(traits.may_block());
@@ -51,7 +51,7 @@ TEST(TaskTraitsTest, ThreadPolicy) {
 TEST(TaskTraitsTest, MayBlock) {
   constexpr TaskTraits traits = {MayBlock()};
   EXPECT_FALSE(traits.priority_set_explicitly());
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, traits.priority());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, traits.priority());
   EXPECT_EQ(TaskShutdownBehavior::SKIP_ON_SHUTDOWN, traits.shutdown_behavior());
   EXPECT_EQ(ThreadPolicy::PREFER_BACKGROUND, traits.thread_policy());
   EXPECT_TRUE(traits.may_block());
@@ -61,7 +61,7 @@ TEST(TaskTraitsTest, MayBlock) {
 TEST(TaskTraitsTest, WithBaseSyncPrimitives) {
   constexpr TaskTraits traits = {WithBaseSyncPrimitives()};
   EXPECT_FALSE(traits.priority_set_explicitly());
-  EXPECT_EQ(TaskPriority::USER_VISIBLE, traits.priority());
+  EXPECT_EQ(TaskPriority::USER_BLOCKING, traits.priority());
   EXPECT_EQ(TaskShutdownBehavior::SKIP_ON_SHUTDOWN, traits.shutdown_behavior());
   EXPECT_EQ(ThreadPolicy::PREFER_BACKGROUND, traits.thread_policy());
   EXPECT_FALSE(traits.may_block());

content/browser/scheduler/browser_task_executor_unittest.cc

@@ -118,11 +118,13 @@ class BrowserTaskTraitsMappingTest : public BrowserTaskExecutorTest {
     EXPECT_EQ(GetQueueType({ID, BrowserTaskType::kBootstrap}),
               QueueType::kBootstrap);
     EXPECT_EQ(GetQueueType({ID, BrowserTaskType::kDefault}),
-              QueueType::kDefault);
+              QueueType::kUserBlocking);
     EXPECT_EQ(GetQueueType({ID, BrowserTaskType::kNavigation}),
               QueueType::kNavigationAndPreconnection);
     EXPECT_EQ(GetQueueType({ID, BrowserTaskType::kPreconnect}),
               QueueType::kNavigationAndPreconnection);
+
+    EXPECT_EQ(GetQueueType({ID}), QueueType::kUserBlocking);
   }
 
  private: