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

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index a19fcec3b91ae03254b2c764c93cdd16acb99628..8ae7151772761f06c9eb4c70e6a1e8c9b7a23caa 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -135,6 +135,12 @@ bool LCodeGen::GeneratePrologue() {
   }
 #endif
 
+  const FunctionEntryHook* hook_location = V8::GetFunctionEntryHookLocation();
+  if (*hook_location != NULL) {
+    ProfileEntryHookStub stub;
+    __ CallStub(&stub);
+  }
+
   // Strict mode functions need to replace the receiver with undefined
   // when called as functions (without an explicit receiver
   // object). rcx is zero for method calls and non-zero for function