Always use sized internal formats for textures in TextureGL.
Always use sized internal formats for textures in TextureGL.

On desktop GL, using an internal format of GL_RGBA produces GL_RGBA8
textures even if format is set to GL_FLOAT.  Use sized internal formats
whenever possible to ensure that the internal format of the texture is
the expected format.

Fixes:
 * conformance/extensions/oes-texture-float-with-image-data.htm
 * conformance/extensions/oes-texture-float-with-image.html
 * conformance/extensions/oes-texture-float.html
 * conformance/extensions/oes-texture-half-float-linear.html
 * conformance/extensions/oes-texture-half-float-with-image-data.html
 * conformance/extensions/oes-texture-half-float-with-image.html
 * conformance/extensions/oes-texture-half-float.html

BUG=angleproject:884

Change-Id: I227e782fe9aae7b2e66df67c7a4519cfc79890b9
Reviewed-on: https://chromium-review.googlesource.com/287529
Reviewed-by: Kenneth Russell <1ebccd90c2bc76de65b6f830f2128a91ed69fdfb@chromium.org>
Tested-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

larsbergstrom/angle,vvuk/angle,bsergean/angle,MSOpenTech/angle,csa7mdm/angle,mikolalysenko/angle,ecoal95/angle,mybios/angle,mybios/angle,mikolalysenko/angle,ppy/angle,vvuk/angle,mlfarrell/angle,mlfarrell/angle,ecoal95/angle,crezefire/angle,ecoal95/angle,domokit/waterfall,mikolalysenko/angle,ecoal95/angle,crezefire/angle,bsergean/angle,csa7mdm/angle,larsbergstrom/angle,ecoal95/angle,csa7mdm/angle,crezefire/angle,mikolalysenko/angle,crezefire/angle,bsergean/angle,bsergean/angle,csa7mdm/angle,MSOpenTech/angle,larsbergstrom/angle,mybios/angle,mlfarrell/angle,domokit/waterfall,mlfarrell/angle,MSOpenTech/angle,vvuk/angle,ppy/angle,larsbergstrom/angle,vvuk/angle,mybios/angle,ppy/angle,MSOpenTech/angle,ppy/angle