Allow GetVerdictCacheManager to return nullptr.

Same as GetPasswordProtectionService, it is ok to return nullptr for
GetVerdictCacheManager, since SafeBrowsingService::GetVerdictCacheManager
already returns nullptr when safe browsing is off.

The validity of cache manager is already measured from the caller:
uma/p/chrome/timeline_v2/?sid=c936612232d60ca29d3ad4da77436787

Bug: 1049694
Change-Id: I53016d115bb33ab37dbd6eb78bca08bcaf9cb91c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057864Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Xinghui Lu <xinghuilu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742462}

chrome/browser/safe_browsing/safe_browsing_service.cc

@@ -250,8 +250,11 @@ VerdictCacheManager* SafeBrowsingService::GetVerdictCacheManager(
 
 base::WeakPtr<VerdictCacheManager>
 SafeBrowsingService::GetVerdictCacheManagerWeakPtr(Profile* profile) const {
-  if (profile->GetPrefs()->GetBoolean(prefs::kSafeBrowsingEnabled))
-    return services_delegate_->GetVerdictCacheManager(profile)->GetWeakPtr();
+  if (profile->GetPrefs()->GetBoolean(prefs::kSafeBrowsingEnabled)) {
+    VerdictCacheManager* cache_manager =
+        services_delegate_->GetVerdictCacheManager(profile);
+    return cache_manager ? cache_manager->GetWeakPtr() : nullptr;
+  }
   return nullptr;
 }
 

chrome/browser/safe_browsing/services_delegate.cc

@@ -86,8 +86,7 @@ VerdictCacheManager* ServicesDelegate::GetVerdictCacheManager(
     Profile* profile) const {
   DCHECK(profile);
   auto it = cache_manager_map_.find(profile);
-  DCHECK(it != cache_manager_map_.end());
-  return it->second.get();
+  return it != cache_manager_map_.end() ? it->second.get() : nullptr;
 }
 
 void ServicesDelegate::ShutdownServices() {