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When native GPU memory buffers were enabled we noticed many crashes
reporting mmap failing.

This CL adds fd number to crash report when dmabuf mmap fails, because we think
fd limit may cause this crash.
It's follow-up CL of https://codereview.chromium.org/2710183005/

BUG=629521

Review-Url: https://codereview.chromium.org/2725813005
Cr-Commit-Position: refs/heads/master@{#456154}