Fix validity check in SkSurface::MakeFromBackendTextureAsRenderTarget
Fix validity check in SkSurface::MakeFromBackendTextureAsRenderTarget

Swaped the order of validate_backend_texture() and
SkSurface_Gpu::Valid() so that the pixel config computed by
validate_backend_texture() get used by SkSurface_Gpu::Valid().
This makes the behavior of this method consistent with the behavior
of sister method MakeFromBackendTexture()

BUG=788439

Change-Id: I132ea8da23430ea99bbeabce79b08edb6b4cae03
Reviewed-on: https://skia-review.googlesource.com/141837
Commit-Queue: Justin Novosad <f3637a096339da458baf3149581fbd4001a43e6c@chromium.org>
Reviewed-by: Justin Novosad <f3637a096339da458baf3149581fbd4001a43e6c@google.com>
Reviewed-by: Greg Daniel <39df0a804564ccb6cf75f18db79653821f37c1c5@google.com>
Auto-Submit: Justin Novosad <f3637a096339da458baf3149581fbd4001a43e6c@chromium.org>

rubenvb/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,google/skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,HalCanary/skia-hc,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,google/skia,rubenvb/skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia