Precache manifest should not be added to fetcher pool which is full

components/precache/core/precache_fetcher.cc

Index: components/precache/core/precache_fetcher.cc
diff --git a/components/precache/core/precache_fetcher.cc b/components/precache/core/precache_fetcher.cc
index cfcc3dcffb43c4c109cc7dfa3d5a3b334e24ee79..16effb64d34e3a866d075fe49b50748012a9b219 100644
--- a/components/precache/core/precache_fetcher.cc
+++ b/components/precache/core/precache_fetcher.cc
@@ -46,11 +46,15 @@ const int kNoTracking =
     net::LOAD_DO_NOT_SAVE_COOKIES | net::LOAD_DO_NOT_SEND_COOKIES |
     net::LOAD_DO_NOT_SEND_AUTH_DATA;
 
-namespace {
-
 // The maximum number of URLFetcher requests that can be on flight in parallel.
 const int kMaxParallelFetches = 10;
 
+int GetDefaultMaxParallelFetches() {
+  return kMaxParallelFetches;
+}
+
+namespace {
+
 // The maximum for the Precache.Fetch.ResponseBytes.* histograms. We set this to
 // a number we expect to be in the 99th percentile for the histogram, give or
 // take.
@@ -327,7 +331,7 @@ PrecacheFetcher::PrecacheFetcher(
       config_url_(config_url),
       manifest_url_prefix_(manifest_url_prefix),
       precache_delegate_(precache_delegate),
-      pool_(kMaxParallelFetches),
+      pool_(GetDefaultMaxParallelFetches()),
       experiment_id_(experiment_id) {
   DCHECK(request_context_.get());  // Request context must be non-NULL.
   DCHECK(precache_delegate_);  // Precache delegate must be non-NULL.
@@ -416,14 +420,11 @@ void PrecacheFetcher::StartNextResourceFetch() {
 }
 
 void PrecacheFetcher::StartNextManifestFetch() {
-  if (manifest_urls_to_fetch_.empty())
+  if (manifest_urls_to_fetch_.empty() || !pool_.IsAvailable())
     return;
 
   // We only fetch one manifest at a time to keep the size of
   // resource_urls_to_fetch_ as small as possible.
-  DCHECK(pool_.IsAvailable())
-      << "There are no available parallel requests to fetch the next manifest. "
-         "Did you forget to call Delete?";
   VLOG(3) << "Fetching " << manifest_urls_to_fetch_.front();
   pool_.Add(base::WrapUnique(new Fetcher(
       request_context_.get(), manifest_urls_to_fetch_.front(),