add gflags support files from webrtc

files needed for command line support with gtest.
These files are copied directly from webrtc.

TBR=kjellander@chromium.org
BUG=libyuv:507

Review URL: https://codereview.chromium.org/1414483002 .

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1513
+Version: 1514
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1513
+#define LIBYUV_VERSION 1514
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

libyuv_test.gyp

@@ -18,6 +18,15 @@
       'dependencies': [
         'libyuv.gyp:libyuv',
         'testing/gtest.gyp:gtest',
+        'third_party/gflags/gflags.gyp:gflags',
+      ],
+      'direct_dependent_settings': {
+        'defines': [
+          'GTEST_RELATIVE_PATH',
+        ],
+      },
+      'export_dependent_settings': [
+        '<(DEPTH)/testing/gtest.gyp:gtest',
       ],
       'defines': [
         # Enable the following 3 macros to turn off assembly for specified CPU.