Generate a custom OSR entrypoint for OSR compiles on all platforms, and transition to optimized cod…

src/x64/lithium-codegen-x64.h

Index: src/x64/lithium-codegen-x64.h
diff --git a/src/x64/lithium-codegen-x64.h b/src/x64/lithium-codegen-x64.h
index 65c6dcae1f9793c6e668c03bc894a1115e2e3f56..ba2b2608ce9b0f98f6cd1c330becb952b3bf55dc 100644
--- a/src/x64/lithium-codegen-x64.h
+++ b/src/x64/lithium-codegen-x64.h
@@ -191,6 +191,9 @@ class LCodeGen V8_FINAL BASE_EMBEDDED {
   bool GenerateJumpTable();
   bool GenerateSafepointTable();
 
+  // Generates the custom OSR entrypoint and sets the osr_pc_offset.
+  void GenerateOsrPrologue();
+
   enum SafepointMode {
     RECORD_SIMPLE_SAFEPOINT,
     RECORD_SAFEPOINT_WITH_REGISTERS