cc/blink: Veto checker-imaging for multipart image resources.

cc/tiles/checker_image_tracker.cc

Index: cc/tiles/checker_image_tracker.cc
diff --git a/cc/tiles/checker_image_tracker.cc b/cc/tiles/checker_image_tracker.cc
index e076983ad7e9f3452a042accf35c69efd2895b57..a44bd648937cb9dab0434ae542c63e7c8c923faf 100644
--- a/cc/tiles/checker_image_tracker.cc
+++ b/cc/tiles/checker_image_tracker.cc
@@ -26,12 +26,14 @@ std::string ToString(PaintImage::Id paint_image_id,
                      bool complete,
                      bool static_image,
                      bool fits_size_constraints,
+                     bool is_multi_part,
                      size_t size) {
   std::ostringstream str;
   str << "paint_image_id[" << paint_image_id << "] sk_image_id[" << sk_image_id
       << "] complete[" << complete << "] static[" << static_image
       << "], fits_size_constraints[" << fits_size_constraints << "], size["
-      << size << "]";
+      << size << "]"
+      << " is_multi_part[" << is_multi_part << "]";
   return str.str();
 }
 
@@ -182,15 +184,17 @@ bool CheckerImageTracker::ShouldCheckerImage(const DrawImage& draw_image,
 
     // Only checker images that are static and completely loaded and fit within
     // the size constraints.
-    bool can_checker_image = complete && static_image && fits_size_constraints;
+    bool can_checker_image = complete && static_image &&

[vmpstr, 2017/06/16 17:35:36]

Can you update the comment to state in words when we can checker an image (and
possibly why for cases like multipart)

+                             fits_size_constraints && !image.is_multi_part();
     if (can_checker_image)
       it->second.policy = DecodePolicy::ASYNC;
 
-    TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
-                 "CheckerImageTracker::CheckerImagingDecision",
-                 "can_checker_image", can_checker_image, "image_params",
-                 ToString(image_id, image.sk_image()->uniqueID(), complete,
-                          static_image, fits_size_constraints, size));
+    TRACE_EVENT2(
+        TRACE_DISABLED_BY_DEFAULT("cc.debug"),
+        "CheckerImageTracker::CheckerImagingDecision", "can_checker_image",
+        can_checker_image, "image_params",
+        ToString(image_id, image.sk_image()->uniqueID(), complete, static_image,
+                 fits_size_constraints, image.is_multi_part(), size));
   }
 
   // Update the decode state from the latest image we have seen. Note that it