REPRO STEPS:

1. Add a layout test that triggers a pixel dump of an OOPIF.
   For example - one can patch in https://crrev.com/c/1028368

2. Run the test as follows:

    third_party/blink/tools/run_web_tests.py -t rel http/tests/cross-site-frame.html --no-retry --additional-drt-flag=--site-per-process

EXPECTED BEHAVIOR: The test passes

ACTUAL BEHAVIOR: Renderer hits a DCHECK failure and crashes:

    STDERR: [117889:117889:0425/094810.108590:FATAL:blink_test_runner.cc(653)] Check failed: 0 != snapshot.info().width() (0 vs. 0)
    STDERR: #0 0x7f2d9fb108fc base::debug::StackTrace::StackTrace()
    STDERR: #1 0x7f2d9fa524fb logging::LogMessage::~LogMessage()
    STDERR: #2 0x000000426f08 content::BlinkTestRunner::OnPixelsDumpCompleted()
    STDERR: #3 0x7f2d972c34da test_runner::(anonymous namespace)::CaptureCallback::DidCompositeAndReadback()