gyp: Add dependency on snapshot.gyp:snapshot after 8bc6219.

Commit 8bc6219 ("[Tizen][Linux] Support getting thumbnail for devtools")
adds a call to ui::GrabViewSnapshotAsync but did not add a dependency on
the ui gyp target that contains the implementation of that function.

This broke the build of xwalk_browsertest on Linux when building with
component=shared_library:

  obj/xwalk/libxwalk_runtime.a(obj/xwalk/runtime/browser/devtools/xwalk_runtime.xwalk_devtools_delegate.o):xwalk_devtools_delegate.cc:function xwalk::XWalkDevToolsDelegate::GetPageThumbnailData(GURL const&):
  error: undefined reference to 'ui::GrabViewSnapshotAsync(aura::Window*, gfx::Rect const&, scoped_refptr<base::TaskRunner>, base::Callback<void (scoped_refptr<base::RefCountedBytes>)> const&)'

Fix it by adding the missing dependency.
[Tizen] packaging: Use the system's YASM instead of Chromium's.

This allows us to get rid of yet another bundled dependency that takes
time to build.

The YASM version shipped by Tizen (1.2.0) is the same one bundled in
Chromium, and the additional patches the latter has are of no relevance
to Tizen.

BUG=XWALK-1985
Merge pull request #2607 from rakuco/tizen-system-yasm

[Tizen] packaging: Use the system's YASM instead of Chromium's.
Merge pull request #2606 from rakuco/shared-library-build-fix

gyp: Add dependency on snapshot.gyp:snapshot after 8bc6219.