CacheStorage: Enable parallel reads on android.

Parallel reads were originally disabled on android due to trial data
showing it regressed cache miss times.  Further analysis of UMA
suggests that there is an abnormally high cache miss volume on
android.  It seems some site is spamming misses and increased
throughput leads to simply greater volume.  There is not much we can
do about this and we should not let it block shipping improvements
that can benefit well behaved sites.

This CL brings the android config in line with other platforms and
permits 16 parallel cache_storage read operations.

Bug: 985379,1007994
Change-Id: Ia0bda728242f1445a9116306c8a26b49b4534e30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2096975Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748829}

content/browser/cache_storage/cache_storage_scheduler.cc

@@ -25,13 +25,7 @@ namespace {
 // Maximum parallel shared operations.  This constant was selected via
 // experimentation.  We tried 4, 16, and 64 for the limit.  16 was clearly
 // better than 4, but 64 was did not provide significant further benefit.
-// TODO(crbug/1007994): Enable parallel shared operations on android after
-//                      performance regressions are addressed.
-#if defined(OS_ANDROID)
-constexpr int kDefaultMaxSharedOps = 1;
-#else
 constexpr int kDefaultMaxSharedOps = 16;
-#endif
 
 const base::FeatureParam<int> kCacheStorageMaxSharedOps{
     &features::kCacheStorageParallelOps, "max_shared_ops",