Add a comment on PRODUCT_STRING_PATH usage in chrome_elf.

chrome_elf/chrome_elf_constants.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome_elf/chrome_elf_constants.h"
 
 #if defined(GOOGLE_CHROME_BUILD)
+// Using PRODUCT_STRING_PATH is wrong as it makes Google Chrome and Canary

[robertshield, 2016/01/25 22:21:03]

Suggest "Using PRODUCT_STRING_PATH will make Google Chrome and Canary
configurations collide. This was deemed to be the best option due to ELF's
inability to depend on BrowserDistribution. http://crbug.com/577820".

It's only wrong if there's a better overall option, which it doesn't look like
there is in this case.

[gab, 2016/01/26 02:14:55]

Done.
The "better" option is to turn the portion of installer_util which is not chrome
specific into a component, but that is far from done, so yea no clean short term
solution (short of duplicating more code to figure out SxS in ELF).

Given I assume the BL's config is fairly stable and would only be used to
rollback all channels in case of emergency it's probably okay.

+// configurations collide but this was still deemed the best option for Chrome
+// ELF per inability to depend on BrowserDistribution. http://crbug.com/577820
 #define PRODUCT_STRING_PATH L"Google\\Chrome"
 #elif defined(CHROMIUM_BUILD)
 #define PRODUCT_STRING_PATH L"Chromium"
 #else
 #error Unknown branding
 #endif
 
 namespace blacklist {
 
 const wchar_t kRegistryBeaconPath[] =
     L"SOFTWARE\\" PRODUCT_STRING_PATH L"\\BLBeacon";
 const wchar_t kRegistryFinchListPath[] =
     L"SOFTWARE\\" PRODUCT_STRING_PATH L"\\BLFinchList";
 const wchar_t kBeaconVersion[] = L"version";
 const wchar_t kBeaconState[] = L"state";
 const wchar_t kBeaconAttemptCount[] = L"failed_count";
 
 const DWORD kBeaconMaxAttempts = 2;
 
 }  // namespace blacklist