Let me try to summarize:
* Goal: Enable VAVDA for Linux
* Problem: libva driver library need to be dlopened before sandboxing, ChromeOS is using hard code driver path. But for linux the driver path differs for different distros, hard code is impossible.
 * Ubuntu/Debain 64: /usr/lib/x86_64-linux-gnu/dri/i965_drv_video.so
 * Ubuntu/Debain 32: /usr/lib/i386-linux-gnu/dri/i965_drv_video.so
 * Tizen(32bit): /usr/lib/dri/i965_dri.so
 * Fedora/Mandriva 64: /usr/lib64/va/drivers/i965_drv_video.so
 * Fedora/Mandriva 32: /usr/lib/va/drivers/i965_drv_video.so (guessing)
 * ChromeOS 64: /usr/lib64/va/drivers/i965_drv_video.so
 * ChromeOS 32: /usr/lib/va/drivers/i965_drv_video.so
* Solutions:
 * S1(current PR looks like): Call vaInitialize() at PreSandbox stage, the driver will be loaded automatically. 
    * Pros: Works on general linux including ChromeOS
    * Cons: Ideally performance concern call `vaInitialize()` than hard code solution.
 * S2(proposed by @tmpsantos): Determine the driver patch during GYP time.
    * Pros: The performance should be same as ChromeOS hard code one.
    * Cons: The driver parent name can be determined via `pkg-config`, but the driver name still need call `vaGetDriverName()`. Otherwise need hard code again, then it won't work on general linux, which means the goal won't achieved. 
* Background: VAVDA is only enabled on ChromeOS and windows on upstream, so the hard coding solution does make sense. Details at https://codereview.chromium.org/15955009/.