TopSites: Clear thumbnails from the cache when their URLs get removed

We already cleared the thumbnails from persistent storage, but they
remained in the in-memory cache, so they remained accessible (until the
next Chrome restart) even after all browsing data was cleared.

Bug: 758169
Change-Id: Id916d22358430a82e6d5043ac04fa463a32f824f
Reviewed-on: https://chromium-review.googlesource.com/758640
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514861}
void TopSitesImpl::RemoveTemporaryThumbnailByURL(const GURL& url) {
  for (TempImages::iterator i = temp_images_.begin(); i != temp_images_.end();
       ++i) {
    if (i->first == url) {
      temp_images_.erase(i);
      return;
    }
  }
}

void TopSitesImpl::RemoveTemporaryThumbnailByURL(const GURL& url) {
  for (TempImages::iterator i = temp_images_.begin(); i != temp_images_.end();
       ++i) {
    if (i->first == url) {
      temp_images_.erase(i);
      return;
    }
  }
}
