Reland of Mojo: Eliminate duplicate C API symbols

mojo/mojo_edk.gyp

Index: mojo/mojo_edk.gyp
diff --git a/mojo/mojo_edk.gyp b/mojo/mojo_edk.gyp
index 9014ee498be9683312927ba58347069d27c96ce5..fb281861b7ea86b94e66b3b862110255a1014a08 100644
--- a/mojo/mojo_edk.gyp
+++ b/mojo/mojo_edk.gyp
@@ -3,9 +3,9 @@
 # found in the LICENSE file.
 
 {
-  'includes': [
-    'mojo_variables.gypi',
-  ],
+  'variables': {
+    'chromium_code': 1,
+  },
   'target_defaults' : {
     'include_dirs': [
       '..',
@@ -54,13 +54,11 @@
         '../base/base.gyp:base',
         '../base/third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',
         '../crypto/crypto.gyp:crypto',
-        'mojo_public.gyp:mojo_system_headers',
+        'mojo_public.gyp:mojo_public_system',
         'mojo_system_ports',
       ],
       'defines': [
         'MOJO_SYSTEM_IMPL_IMPLEMENTATION',
-        'MOJO_SYSTEM_IMPLEMENTATION',
-        'MOJO_USE_SYSTEM_IMPL',
       ],
       'sources': [
         'edk/embedder/configuration.h',
@@ -148,10 +146,6 @@
         'edk/embedder/test_embedder.cc',
         'edk/embedder/test_embedder.h',
       ],
-      'all_dependent_settings': {
-        # Ensures that dependent projects import the core functions on Windows.
-        'defines': ['MOJO_USE_SYSTEM_IMPL'],
-      },
       'conditions': [
         ['OS=="android"', {
           'dependencies': [