Remove error handling from MipmapUtil and add DCHECKs

MipmapUtil had error handling where it would return "-1" values to
indicate errors. None of the call sites should trigger this behavior,
so the error checks were converted to DCHECKs.

R=vmpstr
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2105903003
Cr-Commit-Position: refs/heads/master@{#403285}

cc/tiles/mipmap_util.cc

@@ -22,10 +22,10 @@ int MipMapUtil::GetLevelForSize(const gfx::Size& src_size,
   int src_width = src_size.width();
   int target_height = target_size.height();
   int target_width = target_size.width();
-  bool target_invalid = target_height == 0 || target_width == 0;
-  bool src_invalid = src_height == 0 || src_width == 0;
-  if (target_invalid || src_invalid)
-    return -1;
+  DCHECK_GT(target_height, 0);
+  DCHECK_GT(target_width, 0);
+  DCHECK_GT(src_width, 0);
+  DCHECK_GT(src_height, 0);
 
   int next_mip_height = src_height;
   int next_mip_width = src_width;
@@ -52,8 +52,9 @@ int MipMapUtil::GetLevelForSize(const gfx::Size& src_size,
 
 SkSize MipMapUtil::GetScaleAdjustmentForLevel(const gfx::Size& src_size,
                                               int mip_level) {
-  if (src_size.width() == 0 || src_size.height() == 0 || mip_level == -1)
-    return SkSize::Make(-1, -1);
+  DCHECK_GT(src_size.width(), 0);
+  DCHECK_GT(src_size.height(), 0);
+  DCHECK_GE(mip_level, 0);
 
   gfx::Size target_size = GetSizeForLevel(src_size, mip_level);
 
@@ -64,8 +65,9 @@ SkSize MipMapUtil::GetScaleAdjustmentForLevel(const gfx::Size& src_size,
 
 gfx::Size MipMapUtil::GetSizeForLevel(const gfx::Size& src_size,
                                       int mip_level) {
-  if (src_size.width() == 0 || src_size.height() == 0 || mip_level == -1)
-    return gfx::Size(-1, -1);
+  DCHECK_GT(src_size.width(), 0);
+  DCHECK_GT(src_size.height(), 0);
+  DCHECK_GE(mip_level, 0);
 
   return gfx::Size(ScaleAxisToMipLevel(src_size.width(), mip_level),
                    ScaleAxisToMipLevel(src_size.height(), mip_level));

cc/tiles/mipmap_util.h

@@ -16,25 +16,25 @@ class CC_EXPORT MipMapUtil {
   // Determine the smallest mip level that is larger than |target_size|. Each
   // mip level corresponds to a power of two scale of the image - for instance,
   // level 0 is original size, level 1 is 2x smaller, level 2 is 4x smaller,
-  // etc...
-  // Returns -1 if |src_size| or |target_size| is invalid (any dimension is 0).
+  // etc... This function does not do error checking and must be called with a
+  // valid src_size (width/height > 0) and mip_level (>= 0).
   static int GetLevelForSize(const gfx::Size& src_size,
                              const gfx::Size& target_size);
 
-  // Determines the scale factor for the given |mip_level|. Returns (-1, -1) if
-  // |src_size| is invalid (width/height <= 0), or if mip_level is invalid (==
-  // -1).
+  // Determines the scale factor for the given |mip_level|. This function does
+  // not do error checking and must be called with a valid src_size
+  // (width/height > 0) and mip_level (>= 0).
   static SkSize GetScaleAdjustmentForLevel(const gfx::Size& src_size,
                                            int mip_level);
 
-  // Determine the size of the given |mip_level|. Returns (-1, -1) if
-  // |src_size| is invalid (width/height <= 0) or if mip-level is invalid (==
-  // -1).
+  // Determine the size of the given |mip_level|. This function does not do
+  // error checking and must be called with a valid src_size (width/height > 0)
+  // and mip_level (>= 0).
   static gfx::Size GetSizeForLevel(const gfx::Size& src_size, int mip_level);
 
   // Determines the scale factor for the smallest mip level that is larger than
-  // |target_size|. Returns (-1, -1) if |src_size| or |target_size| is invalid
-  // (width/height <= 0).
+  // |target_size|. This function does not do error checking and must be called
+  // with a valid src_size (width/height > 0) and mip_level (>= 0).
   static SkSize GetScaleAdjustmentForSize(const gfx::Size& src_size,
                                           const gfx::Size& target_size);
 };

cc/tiles/mipmap_util_unittest.cc

@@ -116,34 +116,5 @@ TEST(MipMapUtilTest, Rounding) {
       MipMapUtil::GetScaleAdjustmentForSize(src_size, target_size_smaller));
 }
 
-// Ensures that we return invalid values correctly.
-TEST(MipMapUtilTest, Invalid) {
-  const gfx::Size valid_size(1024, 1024);
-  const gfx::Size invalid_size(0, 1024);
-  const gfx::Size invalid_result_size(-1, -1);
-  const SkSize invalid_float_result_size = SkSize::Make(-1, -1);
-  const int invalid_result_level = -1;
-
-  EXPECT_EQ(invalid_result_level,
-            MipMapUtil::GetLevelForSize(valid_size, invalid_size));
-  EXPECT_EQ(invalid_result_level,
-            MipMapUtil::GetLevelForSize(invalid_size, valid_size));
-  EXPECT_FLOAT_SIZE_EQ(
-      invalid_float_result_size,
-      MipMapUtil::GetScaleAdjustmentForSize(valid_size, invalid_size));
-  EXPECT_FLOAT_SIZE_EQ(
-      invalid_float_result_size,
-      MipMapUtil::GetScaleAdjustmentForSize(invalid_size, valid_size));
-  EXPECT_SIZE_EQ(invalid_result_size,
-                 MipMapUtil::GetSizeForLevel(valid_size, invalid_result_level));
-  EXPECT_SIZE_EQ(invalid_result_size,
-                 MipMapUtil::GetSizeForLevel(invalid_size, 0));
-  EXPECT_FLOAT_SIZE_EQ(invalid_float_result_size,
-                       MipMapUtil::GetScaleAdjustmentForLevel(invalid_size, 0));
-  EXPECT_FLOAT_SIZE_EQ(
-      invalid_float_result_size,
-      MipMapUtil::GetScaleAdjustmentForLevel(valid_size, invalid_result_level));
-}
-
 }  // namespace
 }  // namespace cc

cc/tiles/software_image_decode_controller.cc

@@ -818,7 +818,6 @@ ImageDecodeControllerKey ImageDecodeControllerKey::FromDrawImage(
   if (quality == kMedium_SkFilterQuality && !target_size.IsEmpty()) {
     SkSize mip_target_size =
         MipMapUtil::GetScaleAdjustmentForSize(src_rect.size(), target_size);
-    DCHECK(mip_target_size.width() != -1.f && mip_target_size.height() != -1.f);
     target_size.set_width(src_rect.width() * mip_target_size.width());
     target_size.set_height(src_rect.height() * mip_target_size.height());
   }