[platform] Add NumberOfAvailableBackgroundThreads

include/v8-platform.h

Index: include/v8-platform.h
diff --git a/include/v8-platform.h b/include/v8-platform.h
index 4fbef0f5d96bb49ce6a473d715145f614023224a..11f8d51f02573e1f3ea32a2efba21635ffa25e6d 100644
--- a/include/v8-platform.h
+++ b/include/v8-platform.h
@@ -5,6 +5,7 @@
 #ifndef V8_V8_PLATFORM_H_
 #define V8_V8_PLATFORM_H_
 
+#include <stddef.h>
 #include <stdint.h>
 
 namespace v8 {
@@ -56,6 +57,15 @@ class Platform {
   virtual ~Platform() {}
 
   /**
+   * Gets the number of threads that are used to execute background tasks. Is
+   * used to estimate the number of tasks a work package should be split into.
+   * A return value of 0 means that there are no background threads available.
+   * Note that a value of 0 won't prohibit V8 from posting tasks using
+   * |CallOnBackgroundThread|.
+   */
+  virtual size_t NumberOfAvailableBackgroundThreads() { return 0; }
+
+  /**
    * Schedules a task to be invoked on a background thread. |expected_runtime|
    * indicates that the task will run a long time. The Platform implementation
    * takes ownership of |task|. There is no guarantee about order of execution