Reland "Suppress two canvas layout tests to roll Skia rect blur changes"

This is a reland of 23a46517

These tests will be changing slightly again.

Original change's description:
> Suppress two canvas layout tests to roll Skia rect blur changes
>
> Bug: 990918
> Change-Id: I766e507d5173f847b95ae94bdc2b3857913ec9bb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1754542
> Auto-Submit: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Cr-Commit-Position: refs/heads/master@{#686955}

Bug: 990918
Change-Id: I88ca5e26e889e588f84c0abfabd4a842a98a4e79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1758337Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Cr-Commit-Position: refs/heads/master@{#688495}

third_party/blink/web_tests/TestExpectations

@@ -5255,6 +5255,10 @@ crbug.com/766404 [ Mac ] plugins/keyboard-events.html [ Pass Failure ]
 # This was previously skipped on Windows in the section for crbug.com/757165
 crbug.com/775957 virtual/gpu/fast/canvas/canvas-incremental-repaint.html [ Skip ]
 
+# Canvas tests that are affected by change to Skia GPU rect shadow rendering.
+crbug.com/990918 virtual/gpu/fast/canvas/canvas-shadow-source-in.html [ Pass Failure ]
+crbug.com/990918 virtual/gpu/fast/canvas/canvas-composite-shadow.html [ Pass Failure ]
+
 # Sheriff failures 2017-09-21
 crbug.com/767469 http/tests/navigation/start-load-during-provisional-loader-detach.html [ Pass Failure ]
 crbug.com/767469 virtual/blink-cors/http/tests/navigation/start-load-during-provisional-loader-detach.html [ Pass Failure ]