Override content::CreateInProcessGpuThread for EFL port.

Override content::CreateInProcessGpuThread for EFL port.

Patch makes use of the same override technique used by
RenderThemeChromiumDefault to override the theme method.

Basically, we "redefined" the method we want to override
and include the original source file containing its definition
(.cc or .cpp). Additionally, we exclude the original
implementation file from the build (in GYP).
Then we can have our own implementation of this method
from our efl specific method.

Together with: Iac24e6d38174d7dc8f0d1bb1c37bc8dac05d83c5

Change-Id: Ib7c2aeedbf76de576a25ad95d5437919fec09d3c
Signed-off-by: Antonio Gomes <a1.gomes@samsung.com>