Add a mimeHandler extension API.

extensions/common/api/api.gyp

Index: extensions/common/api/api.gyp
diff --git a/extensions/common/api/api.gyp b/extensions/common/api/api.gyp
index e9d07deddf47c7d4ecf5443b99fb543876be51f6..e242411cc2ba223ecdb92e1befa5260986ad17e6 100644
--- a/extensions/common/api/api.gyp
+++ b/extensions/common/api/api.gyp
@@ -5,6 +5,20 @@
 {
   'targets': [
     {
+      # GN version: //extensions/common/api:mojom
+      'target_name': 'extensions_api_mojom',
+      # The type of this target must be none. This is so that resources can
+      # depend upon this target for generating the js bindings files. Any
+      # generated cpp files must be listed explicitly in chrome_api.
+      'type': 'none',
+      'includes': [
+        '../../../mojo/mojom_bindings_generator.gypi',
+      ],
+      'sources': [
+        'mime_handler.mojom',
+      ],
+    },
+    {
       # GN version: //extensions/common/api
       'target_name': 'extensions_api',
       'type': 'static_library',
@@ -15,6 +29,13 @@
         '../../../build/json_schema_compile.gypi',
         'schemas.gypi',
       ],
+      'dependencies': [
+        'extensions_api_mojom',
+      ],
+      'sources': [
+        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/api/mime_handler.mojom.cc',
+        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/api/mime_handler.mojom.h',
+      ],
     },
     {
       # Protobuf compiler / generator for chrome.cast.channel-related protocol buffers.