cc: Prevent recursion in *TileTaskWorkerPool methods.

cc/resources/pixel_buffer_tile_task_worker_pool.cc

Index: cc/resources/pixel_buffer_tile_task_worker_pool.cc
diff --git a/cc/resources/pixel_buffer_tile_task_worker_pool.cc b/cc/resources/pixel_buffer_tile_task_worker_pool.cc
index 7256f948ead155f4ac4156396ed9292fbc9c76d1..83b6da874ae560b0e2e3f5f4f7c9a3f7c4592f1b 100644
--- a/cc/resources/pixel_buffer_tile_task_worker_pool.cc
+++ b/cc/resources/pixel_buffer_tile_task_worker_pool.cc
@@ -10,6 +10,7 @@
 #include "base/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "base/strings/stringprintf.h"
+#include "cc/base/util.h"
 #include "cc/debug/traced_value.h"
 #include "cc/resources/raster_buffer.h"
 #include "cc/resources/resource.h"
@@ -113,7 +114,8 @@ PixelBufferTileTaskWorkerPool::PixelBufferTileTaskWorkerPool(
     ContextProvider* context_provider,
     ResourceProvider* resource_provider,
     size_t max_transfer_buffer_usage_bytes)
-    : task_runner_(task_runner),
+    : single_entry_holder(false),
+      task_runner_(task_runner),
       task_graph_runner_(task_graph_runner),
       namespace_token_(task_graph_runner->GetNamespaceToken()),
       context_provider_(context_provider),
@@ -153,6 +155,7 @@ void PixelBufferTileTaskWorkerPool::SetClient(TileTaskRunnerClient* client) {
 
 void PixelBufferTileTaskWorkerPool::Shutdown() {
   TRACE_EVENT0("cc", "PixelBufferTileTaskWorkerPool::Shutdown");
+  ScopedSingleEntry scoped_single_entry(&single_entry_holder);
 
   shutdown_ = true;
 
@@ -180,6 +183,7 @@ void PixelBufferTileTaskWorkerPool::Shutdown() {
 
 void PixelBufferTileTaskWorkerPool::ScheduleTasks(TileTaskQueue* queue) {
   TRACE_EVENT0("cc", "PixelBufferTileTaskWorkerPool::ScheduleTasks");
+  ScopedSingleEntry scoped_single_entry(&single_entry_holder);
 
   if (should_notify_client_if_no_tasks_are_pending_.none())
     TRACE_EVENT_ASYNC_BEGIN0("cc", "ScheduledTasks", this);
@@ -277,6 +281,7 @@ void PixelBufferTileTaskWorkerPool::ScheduleTasks(TileTaskQueue* queue) {
 
 void PixelBufferTileTaskWorkerPool::CheckForCompletedTasks() {
   TRACE_EVENT0("cc", "PixelBufferTileTaskWorkerPool::CheckForCompletedTasks");
+  ScopedSingleEntry scoped_single_entry(&single_entry_holder);
 
   CheckForCompletedRasterizerTasks();
   CheckForCompletedUploads();
@@ -441,6 +446,7 @@ void PixelBufferTileTaskWorkerPool::CheckForCompletedUploads() {
 void PixelBufferTileTaskWorkerPool::CheckForCompletedRasterTasks() {
   TRACE_EVENT0("cc",
                "PixelBufferTileTaskWorkerPool::CheckForCompletedRasterTasks");
+  ScopedSingleEntry scoped_single_entry(&single_entry_holder);
 
   // Since this function can be called directly, cancel any pending checks.
   check_for_completed_raster_task_notifier_.Cancel();