blink/canvas: Limit cleanup tasks for locked images.

Don't queue a cleanup task if one is already pending. This avoid
queueing multiple redundant tasks for the case where images are being
purged mid-draw due to exceeding budget constraints.

R=fserb@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I17ba7c59ee6031bf2c18f81e3691685a78634f3c
Bug: 876001, 872117
Reviewed-on: https://chromium-review.googlesource.com/1182601Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584759}

third_party/blink/renderer/platform/graphics/canvas_resource_provider.cc

@@ -544,15 +544,21 @@ void CanvasResourceProvider::CanvasImageProvider::ReleaseLockedImages() {
 
 void CanvasResourceProvider::CanvasImageProvider::CanUnlockImage(
     ScopedDecodedDrawImage image) {
-  if (locked_images_.empty()) {
+  if (!cleanup_task_pending_) {
+    cleanup_task_pending_ = true;
     Platform::Current()->CurrentThread()->GetTaskRunner()->PostTask(
-        FROM_HERE, base::BindOnce(&CanvasImageProvider::ReleaseLockedImages,
+        FROM_HERE, base::BindOnce(&CanvasImageProvider::CleanupLockedImages,
                                   weak_factory_.GetWeakPtr()));
   }
 
   locked_images_.push_back(std::move(image));
 }
 
+void CanvasResourceProvider::CanvasImageProvider::CleanupLockedImages() {
+  cleanup_task_pending_ = false;
+  ReleaseLockedImages();
+}
+
 CanvasResourceProvider::CanvasResourceProvider(
     const IntSize& size,
     const CanvasColorParams& color_params,

third_party/blink/renderer/platform/graphics/canvas_resource_provider.h

@@ -185,7 +185,9 @@ class PLATFORM_EXPORT CanvasResourceProvider
 
    private:
     void CanUnlockImage(ScopedDecodedDrawImage);
+    void CleanupLockedImages();
 
+    bool cleanup_task_pending_ = false;
     std::vector<ScopedDecodedDrawImage> locked_images_;
     cc::PlaybackImageProvider playback_image_provider_;