mark fakes used in gcp_unittests lto_visibility_public

gcp_unittests makes a call across DLL boundaries to register fake
implementations for testing. This is not visible to link-time
optimization, so the classes involved need to be marked
lto_visibility_public to prevent the optimizer from generating
invalid code. See https://clang.llvm.org/docs/LTOVisibility.html

BUG=928396

Change-Id: Ie02e72503b3da8f9c35074bb7c2291d860baba42
Reviewed-on: https://chromium-review.googlesource.com/c/1455095Reviewed-by: Reid Kleckner <rnk@chromium.org>
Reviewed-by: Roger Tawa <rogerta@chromium.org>
Auto-Submit: Bob Haarman <inglorion@chromium.org>
Commit-Queue: Bob Haarman <inglorion@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630446}

chrome/credential_provider/gaiacp/os_process_manager.h

@@ -24,7 +24,7 @@ class ScopedProcessInformation;
 namespace credential_provider {
 
 // Manages OS processes and process attributes.
-class OSProcessManager {
+class [[clang::lto_visibility_public]] OSProcessManager {
  public:
   static OSProcessManager* Get();
 

chrome/credential_provider/gaiacp/os_user_manager.h

@@ -13,7 +13,7 @@ typedef wchar_t* BSTR;
 namespace credential_provider {
 
 // Manages OS users on the system.
-class OSUserManager {
+class [[clang::lto_visibility_public]] OSUserManager {
  public:
   // Minimum length for password buffer when calling GenerateRandomPassword().
   static const int kMinPasswordLength = 24;

chrome/credential_provider/gaiacp/scoped_lsa_policy.h

@@ -14,7 +14,7 @@ namespace credential_provider {
 
 class FakeScopedLsaPolicyFactory;
 
-class ScopedLsaPolicy {
+class [[clang::lto_visibility_public]] ScopedLsaPolicy {
  public:
   static std::unique_ptr<ScopedLsaPolicy> Create(ACCESS_MASK mask);