[dawn][emscripten] Use chromium mirror of emsdk.

- Now that we have a chromium mirror of emsdk, use it in preparations
  to update builders to build wasm targets.

Change-Id: Ia372e670375387867da1ede76179c689c022f4ce
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/242275
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Loko Kung <lokokung@google.com>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
diff --git a/.gitmodules b/.gitmodules
index 02e07a7..bf9bd6d 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -148,7 +148,7 @@
 	gclient-condition = build_with_chromium
 [submodule "third_party/emsdk"]
 	path = third_party/emsdk
-	url = https://github.com/emscripten-core/emsdk.git
+	url = https://chromium.googlesource.com/external/github.com/emscripten-core/emsdk.git
 	gclient-condition = dawn_wasm
 [submodule "third_party/node-api-headers"]
 	path = third_party/node-api-headers
diff --git a/DEPS b/DEPS
index d95dd7e..2e64573 100644
--- a/DEPS
+++ b/DEPS
@@ -366,7 +366,7 @@
 
   # Dependencies required to build / run WebAssembly bindings
   'third_party/emsdk': {
-    'url': '{github_git}/emscripten-core/emsdk.git@419021fa040428bc69ef1559b325addb8e10211f',
+    'url': '{chromium_git}/external/github.com/emscripten-core/emsdk.git@419021fa040428bc69ef1559b325addb8e10211f',
     'condition': 'dawn_wasm',
   },