Implements a new API to set a function entry hook for profiling.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index f8883fc1de96e9839d3ed353597e417a2b69d6c3..4dc6be39ac08b5b569513a12d80e195b1c5b6f03 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -2925,6 +2925,15 @@ typedef uintptr_t (*ReturnAddressLocationResolver)(
 
 
 /**
+ * FunctionEntryHook is the type of the profile entry hook called at entry to
+ * any generated function when function-level profiling is enabled.
+ */
+typedef void (*FunctionEntryHook)(intptr_t function,
+                                  intptr_t stack_pointer,
+                                  uint64_t entry_time);
+
+
+/**
  * Interface for iterating though all external resources in the heap.
  */
 class V8EXPORT ExternalResourceVisitor {  // NOLINT
@@ -3185,6 +3194,20 @@ class V8EXPORT V8 {
       ReturnAddressLocationResolver return_address_resolver);
 
   /**
+   * Allows the host application to provide the address of a function that's
+   * invoked on entry to every V8-generated function.
+   * Note that \p entry_hook is invoked at the very start of each
+   * generated function.
+   *
+   * \param entry_hook a function that will be invoked on entry to every
+   *   V8-generated function.
+   * \returns true on success on supported platforms, false on failure.
+   * \note Setting a new entry hook function when one is already active will
+   *   fail.
+   */
+  static bool SetFunctionEntryHook(FunctionEntryHook entry_hook);
+
+  /**
    * Adjusts the amount of registered external memory.  Used to give
    * V8 an indication of the amount of externally allocated memory
    * that is kept alive by JavaScript objects.  V8 uses this to decide