Add osmesa to GN build.

gpu/gpu.gyp

Index: gpu/gpu.gyp
diff --git a/gpu/gpu.gyp b/gpu/gpu.gyp
index 7d0a8e59b1595a748355390d6859f18636cec257..aa2a8c1bd6582c37a5e6a4d54da3b9416b2f7e91 100644
--- a/gpu/gpu.gyp
+++ b/gpu/gpu.gyp
@@ -12,6 +12,7 @@
   'targets': [
     {
       # Library emulates GLES2 using command_buffers.
+      # GN version: //gpu/command_buffer/client:gles2_implementation
       'target_name': 'gles2_implementation',
       'type': '<(component)',
       'dependencies': [
@@ -32,6 +33,7 @@
       'msvs_disabled_warnings': [4267, ],
     },
     {
+      # GN version: //gpu/command_buffer/client:gl_in_process_context
       'target_name': 'gl_in_process_context',
       'type': '<(component)',
       'dependencies': [
@@ -53,6 +55,7 @@
     },
     {
       # Library emulates GLES2 using command_buffers.
+      # GN version: //gpu/command_buffer/client:gles2_implementation_client_side_arrays
       'target_name': 'gles2_implementation_client_side_arrays',
       'type': '<(component)',
       'defines': [
@@ -100,6 +103,7 @@
     {
       # Stub to expose gles2_implemenation in C instead of C++.
       # so GLES2 C programs can work with no changes.
+      # GN version: //gpu/command_buffer/client:gles2_c_lib
       'target_name': 'gles2_c_lib',
       'type': '<(component)',
       'dependencies': [
@@ -138,6 +142,7 @@
       ],
     },
     {
+      # GN version: //gpu:angle_unittests
       'target_name': 'angle_unittests',
       'type': '<(gtest_target_type)',
       'dependencies': [
@@ -166,6 +171,7 @@
       ],
     },
     {
+      # GN version: //gpu:gpu_unittests
       'target_name': 'gpu_unittests',
       'type': '<(gtest_target_type)',
       'dependencies': [
@@ -190,6 +196,7 @@
         'gles2_c_lib',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'command_buffer/client/buffer_tracker_unittest.cc',
         'command_buffer/client/client_test_helper.cc',
         'command_buffer/client/client_test_helper.h',
@@ -296,6 +303,7 @@
       'msvs_disabled_warnings': [ 4267, ],
     },
     {
+      # GN version: //gpu:gl_tests
       'target_name': 'gl_tests',
       'type': '<(gtest_target_type)',
       'dependencies': [
@@ -323,6 +331,7 @@
         'GL_GLEXT_PROTOTYPES',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'command_buffer/tests/compressed_texture_test.cc',
         'command_buffer/tests/gl_bind_uniform_location_unittest.cc',
         'command_buffer/tests/gl_chromium_framebuffer_multisample_unittest.cc',
@@ -365,6 +374,7 @@
       'msvs_disabled_warnings': [ 4267, ],
     },
     {
+      # GN version: //gpu:test_support
       'target_name': 'gpu_unittest_utils',
       'type': 'static_library',
       'dependencies': [
@@ -389,6 +399,7 @@
     ['component=="static_library"', {
       'targets': [
          {
+          # GN version: //gpu/command_buffer/service:disk_cache_proto
           'target_name': 'disk_cache_proto',
           'type': 'static_library',
           'sources': [ 'command_buffer/service/disk_cache_proto.proto' ],
@@ -399,6 +410,7 @@
           'includes': [ '../build/protoc.gypi' ],
         },
         {
+          # GN version: //gpu
           'target_name': 'gpu',
           'type': 'none',
           'dependencies': [
@@ -416,6 +428,7 @@
           'msvs_disabled_warnings': [4267, ],
         },
         {
+          # GN version: //gpu/command_buffer/common
           'target_name': 'command_buffer_common',
           'type': 'static_library',
           'includes': [
@@ -431,6 +444,7 @@
         },
         {
           # Library helps make GLES2 command buffers.
+          # GN version: //gpu/command_buffer/client:gles2_cmd_helper
           'target_name': 'gles2_cmd_helper',
           'type': 'static_library',
           'includes': [
@@ -443,6 +457,7 @@
           'msvs_disabled_warnings': [4267, ],
         },
         {
+          # GN version: //gpu/command_buffer/client
           'target_name': 'command_buffer_client',
           'type': 'static_library',
           'includes': [
@@ -455,6 +470,7 @@
           'msvs_disabled_warnings': [4267, ],
         },
         {
+          # GN version: //gpu/command_buffer/service
           'target_name': 'command_buffer_service',
           'type': 'static_library',
           'includes': [
@@ -468,6 +484,7 @@
           'msvs_disabled_warnings': [4267, ],
         },
         {
+          # GN version: //gpu/ipc
           'target_name': 'gpu_ipc',
           'type': 'static_library',
           'includes': [
@@ -489,6 +506,7 @@
     { # component != static_library
       'targets': [
          {
+          # GN version: //gpu/command_buffer/service:disk_cache_proto
           'target_name': 'disk_cache_proto',
           'type': 'static_library',
           'sources': [ 'command_buffer/service/disk_cache_proto.proto' ],
@@ -499,6 +517,7 @@
           'includes': [ '../build/protoc.gypi' ],
         },
         {
+          # GN version: //gpu
           'target_name': 'gpu',
           'type': 'shared_library',
           'includes': [
@@ -524,6 +543,7 @@
           'msvs_disabled_warnings': [4267, ],
         },
         {
+          # GN version: //gpu/command_buffer/common
           'target_name': 'command_buffer_common',
           'type': 'none',
           'dependencies': [
@@ -532,6 +552,7 @@
         },
         {
           # Library helps make GLES2 command buffers.
+          # GN version: //gpu/command_buffer/client:gles2_cmd_helper
           'target_name': 'gles2_cmd_helper',
           'type': 'none',
           'dependencies': [
@@ -541,6 +562,7 @@
           'msvs_disabled_warnings': [4267, ],
         },
         {
+          # GN version: //gpu/command_buffer/client
           'target_name': 'command_buffer_client',
           'type': 'none',
           'dependencies': [
@@ -548,6 +570,7 @@
           ],
         },
         {
+          # GN version: //gpu/command_buffer/service
           'target_name': 'command_buffer_service',
           'type': 'none',
           'dependencies': [
@@ -555,6 +578,7 @@
           ],
         },
         {
+          # GN version: //gpu/ipc
           'target_name': 'gpu_ipc',
           'type': 'none',
           'dependencies': [