Move implementation of dart:mojo.internal to mojo/public/platform/dart

mojo/PRESUBMIT.py

Index: mojo/PRESUBMIT.py
diff --git a/mojo/PRESUBMIT.py b/mojo/PRESUBMIT.py
index 0a6429502b4f9b1cf9d4569b1b06d94f8dac689a..2670b311de3430e880f95dbd7c26777794567a68 100644
--- a/mojo/PRESUBMIT.py
+++ b/mojo/PRESUBMIT.py
@@ -112,6 +112,12 @@ def _FindIllegalAbsolutePathsInBuildFiles(input_api, package):
         if package == "EDK":
           continue
 
+        dart_reference_allowed = (f.LocalPath() == "mojo/public/mojo_sdk.gni" or
+            os.path.dirname(f.LocalPath()) == "mojo/public/platform/dart")
+
+        if referenced_path.startswith("//dart") and dart_reference_allowed:
+          continue
+
         # Determine if this is a whitelisted external path.
         if referenced_path in _PACKAGE_WHITELISTED_EXTERNAL_PATHS[package]:
           continue