Implement --ozone-platform flag to select OzonePlatform implementation at runtime

Implement --ozone-platform flag to select OzonePlatform implementation at runtime

This provides a way to select an ozone implementation to use at runtime. Each
ozone implementation adds its name to the ozone_platforms GYP variable, and we
take care of parsing the flag value and configuring chromium to use that
implementation during initialization.

To support external ports, we generate the list of enabled platforms at
build time. The list is a static array that maps values of the --ozone_platform
flag to a constructor function for an OzonePlatform subclass. At runtime, we
call the constructor for platform specified on the command-line and use it to
provide implementations of the various ozone interfaces (SurfaceFactoryOzone,
EventFactoryOzone).

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=232301

[spang, 2013-10-25 19:41:16]

This is the extra goop to let multiple platforms get built into the same binary
with a runtime flag to select one.

[kalyank, 2013-10-25 21:09:30]

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone.gyp
File ui/base/ozone/ozone.gyp (right):

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone.gyp#n...
ui/base/ozone/ozone.gyp:67: }, {  # ozone_platform_dri==0
If ozone is enabled, we always enable ozone_platform_dri and test in
common.gypi. Do we still need ozone_platform_dri = 0 case ?. I mean is it even
possible to have them disabled when support for ozone is enabled.

[spang, 2013-10-25 21:14:14]

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone.gyp
File ui/base/ozone/ozone.gyp (right):

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone.gyp#n...
ui/base/ozone/ozone.gyp:67: }, {  # ozone_platform_dri==0
On 2013/10/25 21:09:30, kalyank wrote:
> If ozone is enabled, we always enable ozone_platform_dri and test in
> common.gypi. Do we still need ozone_platform_dri = 0 case ?. I mean is it even
> possible to have them disabled when support for ozone is enabled.

Yes, because everything from common.gypi is a default value that can be
overridden:

GYP_DEFINES="ozone_platform_dri=0" gclient runhooks

would remove DRI support from the build.

[vignatti (out of this project), 2013-10-28 14:37:11]

On 2013/10/25 19:41:16, spang wrote:
> This is the extra goop to let multiple platforms get built into the same
binary
> with a runtime flag to select one.

this looks very nice! Great work really. LGTM

[rjkroege, 2013-10-28 16:02:14]

lgtm with some nits

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone_platf...
File ui/base/ozone/ozone_platform.cc (right):

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone_platf...
ui/base/ozone/ozone_platform.cc:16: for (int i = 0; i < kOzonePlatformCount;
++i)
default maps to the first element in the list right?

In which case, why not move the platform_name == "default" out of the loop? I
think that would be easier to read.

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone_platf...
ui/base/ozone/ozone_platform.cc:24: std::string GetRequestedPlatform() {
maybe add a comment here saying "returns the name of the ozone platform" or
something

[spang, 2013-10-28 16:27:38]

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone_platf...
File ui/base/ozone/ozone_platform.cc (right):

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone_platf...
ui/base/ozone/ozone_platform.cc:16: for (int i = 0; i < kOzonePlatformCount;
++i)
On 2013/10/28 16:02:15, rjkroege wrote:
> default maps to the first element in the list right?
> 
> In which case, why not move the platform_name == "default" out of the loop? I
> think that would be easier to read.

Done.

https://codereview.chromium.org/44053005/diff/60001/ui/base/ozone/ozone_platf...
ui/base/ozone/ozone_platform.cc:24: std::string GetRequestedPlatform() {
On 2013/10/28 16:02:15, rjkroege wrote:
> maybe add a comment here saying "returns the name of the ozone platform" or
> something

Done.

[kalyank, 2013-10-29 16:59:08]

I am happy with the solution, thanks for handling this. At some point, we should
also update ozone wiki page with a short explanation.

[commit-bot: I haz the power, 2013-10-31 23:23:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/spang@chromium.org/44053005/220001

[commit-bot: I haz the power, 2013-11-01 05:37:33]

Change committed as 232301