cppgc: Add pretty-printers for (cppgc|blink)::Members

No need to use 'cpcp' or 'cpm' now, simple 'print' shall work:
Instead of:
  {
    <cppgc::internal::MemberBase> = {raw_ = {value_ = 2300193596}},
    <cppgc::internal::DisabledCheckingPolicy> = {<No data fields>},
    <No data fields>
  }
the output becomes:
  cppgc::Member<GCed> pointing to 0xbbbbbbbb12345678

Bug: chromium:1373391
Change-Id: I72645d372ee830e20ec02b991ddff94851c4a49f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3948607
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83654}

tools/gdbinit

@@ -279,3 +279,44 @@ document cpm
 Prints member, compressed or not.
 Usage: cpm member
 end
+
+# Pretty printer for cppgc::Member.
+python
+
+import re
+
+
+class CppGCMemberPrinter(object):
+  """Print cppgc Member types."""
+
+  def __init__(self, val, category, pointee_type):
+    self.val = val
+    self.category = category
+    self.pointee_type = pointee_type
+
+  def to_string(self):
+    pointer = gdb.parse_and_eval(
+        "_cppgc_internal_Print_Member((cppgc::internal::MemberBase*){})".format(
+            self.val.address))
+    return "{}Member<{}> pointing to {}".format(
+        '' if self.category is None else self.category, self.pointee_type,
+        pointer)
+
+  def display_hint(self):
+    return "{}Member<{}>".format('' if self.category is None else self.category,
+                                 self.pointee_type)
+
+
+def cppgc_pretty_printers(val):
+  typename = val.type.name or val.type.tag or str(val.type)
+  regex = re.compile("^(cppgc|blink)::(Weak|Untraced)?Member<(.*)>$")
+  match = regex.match(typename)
+  if match is None:
+    return None
+  return CppGCMemberPrinter(
+      val, category=match.group(2), pointee_type=match.group(3))
+
+
+gdb.pretty_printers.append(cppgc_pretty_printers)
+
+end