leveldb: Not logging SharedCache.BytesUsed.InMemory.

A bug was not recording LevelDB.SharedCache.BytesUsed.InMemory
on small memory devices. However, because the in-memory shared
cache size is always zero the correct fix is to simply not
record this value.

Bug: 750798
Change-Id: Ib5e1188aa857aae6510118bb9ccf27e06ac8c8eb
Reviewed-on: https://chromium-review.googlesource.com/723607
Commit-Queue: Chris Mumford <cmumford@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509636}

third_party/leveldatabase/leveldb_chrome.cc

@@ -85,6 +85,9 @@ class Globals {
   void UpdateHistograms() {
     leveldb_env::DBTracker::GetInstance()->UpdateHistograms();
 
+    // In-memory caches are hard-coded to be zero bytes so don't log
+    // LevelDB.SharedCache.BytesUsed.InMemory.
+
     // leveldb limits the read cache size to 1GB, but its default value is 8MB,
     // and Chrome uses either 1MB or 8MB.
     if (GetSharedWebBlockCache() == GetSharedBrowserBlockCache()) {
@@ -96,8 +99,6 @@ class Globals {
                              web_block_cache_->TotalCharge());
     UMA_HISTOGRAM_COUNTS_10M("LevelDB.SharedCache.BytesUsed.Browser",
                              browser_block_cache_->TotalCharge());
-    UMA_HISTOGRAM_COUNTS_10M("LevelDB.SharedCache.BytesUsed.InMemory",
-                             GetSharedInMemoryBlockCache()->TotalCharge());
   }
 
  private: