blink::BlobDataHandle should be thread safe, so use thread safe histogram.

Bug: 780126
Change-Id: I22a0ca4cc6d856cb30cdc767d5135c21ccb4da90
Reviewed-on: https://chromium-review.googlesource.com/747123
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512931}

third_party/WebKit/Source/platform/blob/BlobData.cpp

@@ -400,7 +400,8 @@ BlobDataHandle::BlobDataHandle(const String& uuid,
       size_(size),
       is_single_unknown_size_file_(false) {
   if (RuntimeEnabledFeatures::MojoBlobsEnabled()) {
-    SCOPED_BLINK_UMA_HISTOGRAM_TIMER("Storage.Blob.GetBlobFromUUIDTime");
+    SCOPED_BLINK_UMA_HISTOGRAM_TIMER_THREAD_SAFE(
+        "Storage.Blob.GetBlobFromUUIDTime");
     // TODO(mek): Going through InterfaceProvider to get a BlobRegistryPtr
     // ends up going through the main thread. Ideally workers wouldn't need
     // to do that.