base: Support setting thread priorities generically.

base/base.gypi

Index: base/base.gypi
diff --git a/base/base.gypi b/base/base.gypi
index de000d1d2f4767fb6eb0852f279a091831fcea1b..e76d6e044a92b6b171478770e15c3fed6f7436bc 100644
--- a/base/base.gypi
+++ b/base/base.gypi
@@ -467,6 +467,8 @@
           'threading/non_thread_safe_impl.cc',
           'threading/non_thread_safe_impl.h',
           'threading/platform_thread.h',
+          'threading/platform_thread_android.cc',
+          'threading/platform_thread_linux.cc',
           'threading/platform_thread_mac.mm',
           'threading/platform_thread_posix.cc',
           'threading/platform_thread_win.cc',
@@ -662,6 +664,12 @@
               ['include', '^worker_pool_linux\\.cc$'],
             ],
           }],
+          ['OS == "android" and _toolset == "host" and host_os == "linux"', {
+            'sources/': [
+              # Pull in specific files for host builds.
+              ['include', 'threading/platform_thread_linux.cc$'],
+            ],
+          }],
           ['OS == "ios"', {
             'sources/': [
               # Pull in specific Mac files for iOS (which have been filtered out