Remove higher tolerance in roundtrip ConvertToBlob layout tests for Webp

TBR=fserb@chromium.org

Bug: 847527
Change-Id: I6effeada64f09fb2d0dc549a0de66a1c783915d1
Reviewed-on: https://chromium-review.googlesource.com/1175000Reviewed-by: Mohammad Reza Zakerinasab <zakerinasab@chromium.org>
Commit-Queue: Mohammad Reza Zakerinasab <zakerinasab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583101}

third_party/WebKit/LayoutTests/fast/canvas/color-space/canvas-colorManaged-convertToBlob-roundtrip.html

@@ -13,27 +13,22 @@ var opaqueReferencePxiels, transparentReferencePixels;
 
 function testPixels(actualPixels, refPixels, testScenario)
 {
-    // Plain testing requires a tolerance as high as 50 for 8-8-8-8, which does
+    // Plain testing requires a tolerance as high as 26 for 8-8-8-8, which does
     // not leave that much to test. Instead, we narrow down the source of
     // expected error.
     // - Alpha values should always match.
     // - Color components should be acceptably close, except for the red
     //   channel of the green pixel. Green has the largest change in what's
     //   representable between sRGB and P3/2020.
-    //   Red channel of the green pixel is component numnber 5.
-    // - Webp round-trip results in significant error in the color values.
-    //   crbug.com/847527
+    //   Red channel of the green pixel is R channel of the second pixel.
 
     if (testScenario.canvasColorParam.pixelFormat == '8-8-8-8') {
         let tolerance_color = 10;
         let tolerance_r_green = 26;
-        let tolerance_webp = 50;
         for (let i = 0; i < actualPixels.length; i++) {
             // Alpha channel
             if (i % 4 == 3)
                 assert_equals(actualPixels[i], refPixels[i]);
-            else if (testScenario.encodeOptions.type == 'image/webp')
-                assert_approx_equals(actualPixels[i], refPixels[i], tolerance_webp);
             // Red channel of the green pixel
             else if (i == 4)
                 assert_approx_equals(actualPixels[i], refPixels[i], tolerance_r_green);
@@ -42,13 +37,10 @@ function testPixels(actualPixels, refPixels, testScenario)
         }
     } else {
         let tolerance_color = 0.02;
-        let tolerance_webp = 0.2;
         for (let i = 0; i < actualPixels.length; i++) {
             // Alpha channel
             if (i % 4 == 3)
                 assert_equals(actualPixels[i], refPixels[i]);
-            else if (testScenario.encodeOptions.type == 'image/webp')
-                assert_approx_equals(actualPixels[i], refPixels[i], tolerance_webp);
             else
                 assert_approx_equals(actualPixels[i], refPixels[i], tolerance_color);
         }
@@ -99,7 +91,7 @@ function runConvertToBlobTest(testScenario) {
     drawPatternOnCanvsa(ctx, testScenario.alpha, compositeOverBlack);
     var refPixels = ctx.getImageData(0, 0, 2, 2).dataUnion;
 
-    var t = async_test("Test canvas convertToBlob(): " + 
+    var t = async_test("Test canvas convertToBlob(): " +
         testScenarioToString(testScenario));
 
     var image = new Image();
@@ -115,7 +107,7 @@ function runConvertToBlobTest(testScenario) {
         t.step_func(function(blob) {
             var urlCreator = window.URL || window.webkitURL;
             image.src = urlCreator.createObjectURL(blob);
-        }), 
+        }),
         t.step_func_done(function(e) {
             assert_false("convertToBlob failed.");
         })
@@ -149,7 +141,7 @@ function runAllTests() {
         {colorSpace: 'rec2020', pixelFormat: 'float16'},
         {colorSpace: 'p3', pixelFormat: 'float16'}];
     // crbug.com/859102
-//    var alphaValues = [0.5, 1];
+    // var alphaValues = [0.5, 1];
     var alphaValues = [1];
 
     // The *correct* way to test convertToBlob() is to directly examine the