In short, the PE loader does not explicitly load up the certificate details into the new process at run-time.
In the binary, the certificates are referenced via the IMAGE_DIRECTORY_ENTRY_SECURITY directory; but they are not in a section that is mapped into virtual memory. The data is instead appended to the file.
You might get lucky and find the cert data has been mapped via a memory mapped file, or if you captured a full kernel dump you might have a copy of it. Otherwise you will have to try and source the file from the computer.
Your best bet is to manually compare the code-in-memory to a valid copy of googleupdate.
Also keep in mind that the source binary could be completely valid, but the behavior changed at run-time (via code injection, etc.). So even if you could easily validate the integrity of the certificate, it wouldn't detect rogue threads, hooked functions, etc.