Move to Chromium 38.0.2125.34, the first M38 beta release.

As usual, SIMD support in V8 is disabled while the v8-crosswalk folks
rebase their code.

One important point: on Linux builds, Chromium will now default to using
its bundled clang copy instead of the system's GCC, and Ubuntu 12.04's
GCC is now too old to build the code (at least 4.8.0 is required). Use
of clang can be disabled by passing -Dclang=0 to gyp.

Relevant, non-extensive list of Chromium CLs which required us to adapt
our code:

  * https://codereview.chromium.org/213583003
  * https://codereview.chromium.org/273223002
  * https://codereview.chromium.org/321423002
  * https://codereview.chromium.org/338373002
  * https://codereview.chromium.org/344493002
  * https://codereview.chromium.org/356713005
  * https://codereview.chromium.org/364123002
  * https://codereview.chromium.org/369703002
  * https://codereview.chromium.org/373623002
  * https://codereview.chromium.org/381113004
  * https://codereview.chromium.org/382143005
  * https://codereview.chromium.org/393653002
  * https://codereview.chromium.org/397243004
  * https://codereview.chromium.org/398243002
  * https://codereview.chromium.org/398503002
  * https://codereview.chromium.org/398873004
  * https://codereview.chromium.org/405633002
  * https://codereview.chromium.org/411283002
  * https://codereview.chromium.org/415423002
  * https://codereview.chromium.org/421613002
  * https://codereview.chromium.org/425653002
  * https://codereview.chromium.org/432553003

Relevant intermediate commit messages from intermediate commits in our
next branch:

[Android] Aligh with new java targets' classes_dir

Chromium has changed java targets' classes_dir to
<intermediate>/classes/2.
It impacts xwalk_native_libraries_java and
xwalk_core_library_java in crosswalk. Changes the
classes_dir of these two targets accordingly.

In addition, use dependent settings of gyp to sync variables
between targets instead of hardcode to avoid similar issues in
future.

--

Gardening M38: Remove classes_dir in gyp files

Upstream removes classes_dir in java.gypi and java_apk.gypi.
Previously, crosswalk relies on it to create xwalk_core_library
and xwalk_runtime_embedded.
For xwalk_core_library, use javac_jar_path instead of classes_dir.
For xwalk_runtime_embedded, the target is not used any more
after xwalk_app_template switch to use xwalk_core_library,
just removed it.

--

Gardening M38: Remove classes_dir in gyp files

Upstream removes classes_dir in java.gypi and java_apk.gypi.
Previously, crosswalk relies on it to create xwalk_core_library
and xwalk_runtime_embedded.
For xwalk_core_library, use javac_jar_path instead of classes_dir.
For xwalk_runtime_embedded, the target is not used any more
after xwalk_app_template switch to use xwalk_core_library,
just removed it.

--

Re-enable WebRTC support on Tizen.

Temporarily roll WebRTC's revision manually from c1696da to cdc3123:
cdc3123 Rename linuxwindowpicker to x11windowpicker & only use it with
        use_x11
ee3ec04 common_audio/signal_processing: Remove macro
        WEBRTC_SPL_UMUL_32_16_RSFT16

cdc3123 is required to fix XWALK-2160 and re-enable WebRTC support, as
libjingle now forces a dependency on the webrtc_base target which was
causing the Tizen build to fail even with -Ddisable_webrtc=1.

See https://code.google.com/p/webrtc/issues/detail?id=3625 and
XWALK-2160.

--

gyp_xwalk: Sync with M38's gyp_chromium.

Sync the script with Chromium commits r279309, r286307, r286632,
r288360, r289094, r289099, r289158, r289546 and r289699.

Most of the changes are related to supporting the --analyzer option and
moving the handling of landmines to a separate file.

--

BUG=XWALK-2160
BUG=XWALK-2431