skia: Do not include a source file in another source file.

skia: Do not include a source file in another source file.

That can can a duplication of definition of symbols.

This was exposed by
https://chromium.googlesource.com/chromium/src/+/c87c3d2d949f9ba4f17627dc023b303c75b7635f
in the Mac GN builder with errors like:
duplicate symbol __ZN3gfx27SkMatrixToCGAffineTransformERK8SkMatrix in:
     obj/skia/ext/skia_unittests.skia_utils_mac_unittest.o
     obj/skia/ext/skia.skia_utils_mac.o
 (and more similar issues).

Entries were found with the following command line:

$ g grep include skia/ext | grep mm\"

BUG=444058
TEST=unit_tests
R=thakis@chromium.org

Committed: https://crrev.com/786967e07357b26548fc1c21f131c331053ef6d5
Cr-Commit-Position: refs/heads/master@{#310427}

[tfarina, 2015-01-07 19:57:18]

PTAL

[Nico, 2015-01-07 23:42:05]

The CQ bit was checked by thakis@chromium.org

[Nico, 2015-01-07 23:42:06]

lgtm

[commit-bot: I haz the power, 2015-01-07 23:42:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/832053004/40001

[commit-bot: I haz the power, 2015-01-08 01:18:03]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-01-08 01:19:01]

Patchset 3 (id:??) landed as
https://crrev.com/786967e07357b26548fc1c21f131c331053ef6d5
Cr-Commit-Position: refs/heads/master@{#310427}