gfx: Do the ToEnclosingRect in double precision.

cc/playback/discardable_image_map_unittest.cc

 // Copyright 2015 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.
 
 #include "cc/playback/discardable_image_map.h"
 
 #include <stddef.h>
 
 #include <memory>
 
@@ skipping 387 matching lines @@
                                                            visible_rect.size());
     display_list->Raster(generator.canvas(), nullptr, visible_rect, 1.f);
   }
   std::vector<PositionDrawImage> images =
       GetDiscardableImagesInRect(image_map, gfx::Rect(0, 0, 1, 1));
   EXPECT_EQ(1u, images.size());
   EXPECT_EQ(gfx::Rect(0, 0, dimension, dimension), images[0].image_rect);
 
   images = GetDiscardableImagesInRect(image_map, gfx::Rect(10000, 0, 1, 1));
   EXPECT_EQ(2u, images.size());
-  int expected10k = static_cast<int>(static_cast<float>(dimension - 10000));
-  int expected500 = static_cast<int>(static_cast<float>(dimension - 500));
-  EXPECT_EQ(gfx::Rect(10000, 0, expected10k, dimension), images[1].image_rect);
+  EXPECT_EQ(gfx::Rect(10000, 0, dimension - 10000, dimension),
+            images[1].image_rect);
   EXPECT_EQ(gfx::Rect(0, 0, dimension, dimension), images[0].image_rect);
 
+  // Since we adjust negative offsets before using ToEnclosingRect, the expected
+  // width will be converted to float, which means that we lose some precision.
+  // The expected value is whatever the value is converted to float and then
+  // back to int.
+  int expected10k = static_cast<int>(static_cast<float>(dimension - 10000));
   images = GetDiscardableImagesInRect(image_map, gfx::Rect(0, 500, 1, 1));
   EXPECT_EQ(2u, images.size());
-  EXPECT_EQ(gfx::Rect(0, 500, expected10k, expected500), images[1].image_rect);
+  EXPECT_EQ(gfx::Rect(0, 500, expected10k, dimension - 500),
+            images[1].image_rect);
   EXPECT_EQ(gfx::Rect(0, 0, dimension, dimension), images[0].image_rect);
 }
 
 TEST_F(DiscardableImageMapTest, GetDiscardableImagesRectInBounds) {
   gfx::Rect visible_rect(1000, 1000);
   FakeContentLayerClient content_layer_client;
   content_layer_client.set_bounds(visible_rect.size());
 
   sk_sp<SkImage> discardable_image =
       CreateDiscardableImage(gfx::Size(100, 100));
@@ skipping 26 matching lines @@
   images = GetDiscardableImagesInRect(image_map, gfx::Rect(999, 999, 1, 1));
   EXPECT_EQ(1u, images.size());
   EXPECT_EQ(gfx::Rect(950, 951, 50, 49), images[0].image_rect);
 
   images = GetDiscardableImagesInRect(image_map, gfx::Rect(0, 500, 1, 1));
   EXPECT_EQ(1u, images.size());
   EXPECT_EQ(gfx::Rect(0, 500, 1000, 100), images[0].image_rect);
 }
 
 }  // namespace cc