Adds Mojo IDL.

third_party/WebKit/Source/core/mojo/BUILD.gn

Index: third_party/WebKit/Source/core/mojo/BUILD.gn
diff --git a/third_party/WebKit/Source/core/origin_trials/BUILD.gn b/third_party/WebKit/Source/core/mojo/BUILD.gn
similarity index 55%
copy from third_party/WebKit/Source/core/origin_trials/BUILD.gn
copy to third_party/WebKit/Source/core/mojo/BUILD.gn
index a546bd705c7fa20ab2cd0079412c455f2598ce18..826c971c404b94b07b49c0610e9aa448fb85dbd9 100644
--- a/third_party/WebKit/Source/core/origin_trials/BUILD.gn
+++ b/third_party/WebKit/Source/core/mojo/BUILD.gn
@@ -4,9 +4,17 @@
 
 import("//third_party/WebKit/Source/core/core.gni")
 
-blink_core_sources("origin_trials") {
+blink_core_sources("mojo") {
   sources = [
-    "OriginTrialContext.cpp",
-    "OriginTrialContext.h",
+    "Mojo.cpp",
+    "Mojo.h",
+    "MojoHandle.cpp",
+    "MojoHandle.h",
+    "MojoWatcher.cpp",
+    "MojoWatcher.h",
+  ]
+
+  deps = [
+    "//mojo/public/cpp/system",
   ]
 }