[printing] Print properties backing store value and add a gdb macro for printing LayoutDescriptors.

tools/gdbinit

Index: tools/gdbinit
diff --git a/tools/gdbinit b/tools/gdbinit
index b696a8fc36bd19daf854925a794a0757ce5f8362..cdf2cd4e222a762c645504a89f2038e1a2fa6287 100644
--- a/tools/gdbinit
+++ b/tools/gdbinit
@@ -38,6 +38,15 @@ Print a v8 DescriptorArray object
 Usage: jda tagged_ptr
 end
 
+# Print LayoutDescriptor.
+define jld
+call _v8_internal_Print_LayoutDescriptor((void*)($arg0))
+end
+document jld
+Print a v8 LayoutDescriptor object
+Usage: jld tagged_ptr
+end
+
 # Print TransitionArray.
 define jta
 call _v8_internal_Print_TransitionArray((void*)($arg0))