Record histogram of reason for quads not being put in an overlay.

cc/output/dc_layer_overlay.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_DC_LAYER_OVERLAY_H_
 #define CC_OUTPUT_DC_LAYER_OVERLAY_H_
 
 #include "base/memory/ref_counted.h"
 #include "cc/quads/render_pass.h"
 #include "third_party/skia/include/core/SkColor.h"
@@ skipping 48 matching lines @@
   unsigned filter;
   // If |rpdq| is present, then the renderer must draw the filter effects and
   // copy the result into an IOSurface.
   const RenderPassDrawQuad* rpdq = nullptr;
 };
 
 typedef std::vector<DCLayerOverlay> DCLayerOverlayList;
 
 class DCLayerOverlayProcessor {
  public:
+  // This is used for a histogram to determine why overlays are or aren't
+  // used, so don't remove entries and make sure to update enums.xml if
+  // it changes.
   enum DCLayerResult {
     DC_LAYER_SUCCESS,
+    DC_LAYER_FAILED_UNSUPPORTED_QUAD,
     DC_LAYER_FAILED_QUAD_BLEND_MODE,
     DC_LAYER_FAILED_TEXTURE_NOT_CANDIDATE,
     DC_LAYER_FAILED_OCCLUDED,
-    DC_LAYER_FAILED_UNKNOWN
+    DC_LAYER_FAILED_COMPLEX_TRANSFORM,
+    DC_LAYER_FAILED_MAX,
   };
 
   void Process(ResourceProvider* resource_provider,
                const gfx::RectF& display_rect,
                QuadList* quad_list,
                gfx::Rect* overlay_damage_rect,
                gfx::Rect* damage_rect,
                DCLayerOverlayList* ca_layer_overlays);
   void ClearOverlayState() {
     previous_frame_underlay_rect_ = gfx::Rect();
     previous_occlusion_bounding_box_ = gfx::Rect();
   }
 
  private:
   DCLayerResult FromDrawQuad(ResourceProvider* resource_provider,
                              const gfx::RectF& display_rect,
                              QuadList::ConstIterator quad_list_begin,
                              QuadList::ConstIterator quad,
                              DCLayerOverlay* ca_layer_overlay);
 
   gfx::Rect previous_frame_underlay_rect_;
   gfx::Rect previous_occlusion_bounding_box_;
   gfx::RectF previous_display_rect_;
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_DC_LAYER_OVERLAY_H_