Add tasks traits for BrowserUIThreadScheduler

Add a new task trait to tell the future BrowserUIThreadScheduler which
tasks are critical for startup and allow it to prioritize them
accordingly.

Design doc: https://docs.google.com/document/d/1z1BDq9vzcEpkhN9LSPF5XMnZ0kLJ8mWWkNAi4OI7cos/edit#

Bug: 863341, 872372
Change-Id: Ifb082762726fbda951325802faf82f1dacf219cc
Reviewed-on: https://chromium-review.googlesource.com/c/1454632
Commit-Queue: Carlos Caballero <carlscab@google.com>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629944}

content/public/android/BUILD.gn

@@ -355,6 +355,7 @@ java_cpp_enum("content_public_android_java_enums_srcjar") {
     "//content/browser/android/select_popup.cc",
     "//content/public/browser/android/child_process_importance.h",
     "//content/public/browser/android/motion_event_action.h",
+    "//content/public/browser/browser_task_traits.h",
     "//content/public/browser/browsing_data_remover.h",
     "//content/public/browser/invalidate_type.h",
     "//content/public/browser/navigation_controller.h",

content/public/android/java/src/org/chromium/content/browser/UiThreadTaskTraitsImpl.java

@@ -7,6 +7,7 @@ package org.chromium.content.browser;
 import org.chromium.base.task.TaskPriority;
 import org.chromium.base.task.TaskTraits;
 import org.chromium.content_public.browser.BrowserTaskExecutor;
+import org.chromium.content_public.browser.BrowserTaskType;
 
 /**
  * Provides the implementation needed in UiThreadTaskTraits.
@@ -18,11 +19,14 @@ public class UiThreadTaskTraitsImpl {
     public static final byte EXTENSION_ID = 1;
 
     // Keep in sync with content::BrowserTaskTraitsExtension::Serialize.
-    private static final byte NESTING_INDEX = 1;
+    private static final byte TASK_TYPE = 1;
+    private static final byte NESTING_INDEX = 2;
 
-    private static final byte[] sDefaultExtensionData = getDefaultExtesionData();
+    private static final byte[] sDefaultExtensionData = getDefaultExtensionData();
 
     public static final TaskTraits DEFAULT = new TaskTraits(EXTENSION_ID, sDefaultExtensionData);
+    public static final TaskTraits BOOTSTRAP = new TaskTraits(
+            EXTENSION_ID, getExtensionDataForBrowserTaskType(BrowserTaskType.BOOTSTRAP));
     public static final TaskTraits BEST_EFFORT = DEFAULT.taskPriority(TaskPriority.BEST_EFFORT);
     public static final TaskTraits USER_VISIBLE = DEFAULT.taskPriority(TaskPriority.USER_VISIBLE);
     public static final TaskTraits USER_BLOCKING = DEFAULT.taskPriority(TaskPriority.USER_BLOCKING);
@@ -31,14 +35,22 @@ public class UiThreadTaskTraitsImpl {
         BrowserTaskExecutor.register();
     }
 
-    private static byte[] getDefaultExtesionData() {
+    private static byte[] getDefaultExtensionData() {
         byte extensionData[] = new byte[TaskTraits.EXTENSION_STORAGE_SIZE];
 
         // Note we don't specify the UI thread directly here because it's ID 0 and the array is
         // initialized to zero.
 
+        // Similarly we don't specify BrowserTaskType.Default its ID is also 0.
+
         // TODO(crbug.com/876272) Remove this if possible.
         extensionData[NESTING_INDEX] = 1; // Allow the task to run in a nested RunLoop.
         return extensionData;
     }
+
+    private static byte[] getExtensionDataForBrowserTaskType(int browserTaskType) {
+        byte extensionData[] = getDefaultExtensionData();
+        extensionData[TASK_TYPE] = (byte) browserTaskType;
+        return extensionData;
+    }
 }

content/public/android/java/src/org/chromium/content_public/browser/UiThreadTaskTraits.java

@@ -22,4 +22,5 @@ public class UiThreadTaskTraits {
     public static final TaskTraits BEST_EFFORT = UiThreadTaskTraitsImpl.BEST_EFFORT;
     public static final TaskTraits USER_VISIBLE = UiThreadTaskTraitsImpl.USER_VISIBLE;
     public static final TaskTraits USER_BLOCKING = UiThreadTaskTraitsImpl.USER_BLOCKING;
+    public static final TaskTraits BOOTSTRAP = UiThreadTaskTraitsImpl.BOOTSTRAP;
 }

content/public/browser/browser_task_traits.h

@@ -21,6 +21,21 @@ namespace content {
 // logic for deferred tasks in MessageLoop.
 struct NonNestable {};
 
+// Semantic annotations which tell the scheduler what type of task it's dealing
+// with. This will be used by the scheduler for dynamic prioritization and for
+// attribution in traces, etc...
+// GENERATED_JAVA_ENUM_PACKAGE: org.chromium.content_public.browser
+enum class BrowserTaskType {
+  // A catch all tasks that don't fit the types below.
+  kDefault,
+
+  // Critical startup tasks.
+  kBootstrap,
+
+  // Used to validate values in Java
+  kBrowserTaskType_Last
+};
+
 // TaskTraits for running tasks on the browser threads.
 //
 // These traits enable the use of the //base/task/post_task.h APIs to post tasks
@@ -49,6 +64,7 @@ class CONTENT_EXPORT BrowserTaskTraitsExtension {
     using base::TaskTraits::ValidTrait::ValidTrait;
 
     ValidTrait(BrowserThread::ID);
+    ValidTrait(BrowserTaskType);
     ValidTrait(NonNestable);
   };
 
@@ -59,35 +75,46 @@ class CONTENT_EXPORT BrowserTaskTraitsExtension {
   constexpr BrowserTaskTraitsExtension(ArgTypes... args)
       : browser_thread_(
             base::trait_helpers::GetEnum<BrowserThread::ID>(args...)),
+        task_type_(
+            base::trait_helpers::GetEnum<BrowserTaskType,
+                                         BrowserTaskType::kDefault>(args...)),
         nestable_(!base::trait_helpers::HasTrait<NonNestable>(args...)) {}
 
   // Keep in sync with UiThreadTaskTraits.java
   constexpr base::TaskTraitsExtensionStorage Serialize() const {
-    static_assert(8 == sizeof(BrowserTaskTraitsExtension),
+    static_assert(12 == sizeof(BrowserTaskTraitsExtension),
                   "Update Serialize() and Parse() when changing "
                   "BrowserTaskTraitsExtension");
-    return {kExtensionId,
-            {static_cast<uint8_t>(browser_thread_),
-             static_cast<uint8_t>(nestable_)}};
+    return {
+        kExtensionId,
+        {static_cast<uint8_t>(browser_thread_),
+         static_cast<uint8_t>(task_type_), static_cast<uint8_t>(nestable_)}};
   }
 
   static const BrowserTaskTraitsExtension Parse(
       const base::TaskTraitsExtensionStorage& extension) {
     return BrowserTaskTraitsExtension(
         static_cast<BrowserThread::ID>(extension.data[0]),
-        static_cast<bool>(extension.data[1]));
+        static_cast<BrowserTaskType>(extension.data[1]),
+        static_cast<bool>(extension.data[2]));
   }
 
   constexpr BrowserThread::ID browser_thread() const { return browser_thread_; }
+  constexpr BrowserTaskType task_type() const { return task_type_; }
 
   // Returns true if tasks with these traits may run in a nested RunLoop.
   constexpr bool nestable() const { return nestable_; }
 
  private:
-  BrowserTaskTraitsExtension(BrowserThread::ID browser_thread, bool nestable)
-      : browser_thread_(browser_thread), nestable_(nestable) {}
+  BrowserTaskTraitsExtension(BrowserThread::ID browser_thread,
+                             BrowserTaskType task_type,
+                             bool nestable)
+      : browser_thread_(browser_thread),
+        task_type_(task_type),
+        nestable_(nestable) {}
 
   BrowserThread::ID browser_thread_;
+  BrowserTaskType task_type_;
   bool nestable_;
 };