Fix 3D texture support for generateMipmap in command buffer
Fix 3D texture support for generateMipmap in command buffer

Depth isn't always 1 for 3D texture. This CL make CanGenerateMipmaps()
check depth as well as width and height.

BUG=429053

Review URL: https://codereview.chromium.org/1348253002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#349338}

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