ResourceLoadScheduler: Change only running loader's priority

In DidChangePriority, the last patch changed to check the ClientId,
but it isn't enough to check the running status. This patch adds
a new ResourceLoadScheduler interface to query if the specified
client is in running state.

Bug: 819931
Change-Id: Ibfb6ecc529a21709f144796f5a4c039e2862884e
Reviewed-on: https://chromium-review.googlesource.com/964070Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543630}

third_party/WebKit/Source/platform/loader/fetch/ResourceLoadScheduler.h

@@ -178,6 +178,10 @@ class PLATFORM_EXPORT ResourceLoadScheduler final
   // TrafficReportHints::InvalidInstance() can be used to omit reporting.
   bool Release(ClientId, ReleaseOption, const TrafficReportHints&);
 
+  // Checks if the specified client was already scheduled to call Run(), but
+  // haven't call Release() yet.
+  bool IsRunning(ClientId id) { return running_requests_.Contains(id); }
+
   // Sets outstanding limit for testing.
   void SetOutstandingLimitForTesting(size_t limit) {
     SetOutstandingLimitForTesting(limit, limit);

third_party/WebKit/Source/platform/loader/fetch/ResourceLoader.cpp

@@ -168,8 +168,9 @@ void ResourceLoader::SetDefersLoading(bool defers) {
 
 void ResourceLoader::DidChangePriority(ResourceLoadPriority load_priority,
                                        int intra_priority_value) {
-  if (scheduler_client_id_ != ResourceLoadScheduler::kInvalidClientId) {
+  if (scheduler_->IsRunning(scheduler_client_id_)) {
     DCHECK(loader_);
+    DCHECK_NE(ResourceLoadScheduler::kInvalidClientId, scheduler_client_id_);
     loader_->DidChangePriority(
         static_cast<WebURLRequest::Priority>(load_priority),
         intra_priority_value);