Disable flaky DomSerializerBrowserTests on all platforms
Disable flaky DomSerializerBrowserTests on all platforms

Disables the following two tests:

DomSerializerTests.SerializeHTMLDOMWithNoMetaCharsetInOriginalDoc
DomSerializerTests.SerializeHTMLDOMWithDocType

These tests have been flaky across Windows and Linux builders

BUG=593575
TBR=esprehn@chromium.org

Review URL: https://codereview.chromium.org/1780143002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#380348}

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