git: fix git cache support

It's now based on bot_update logic.

BUG=630601

Review-Url: https://codereview.chromium.org/2209383002

recipe_modules/git/api.py

@@ -213,11 +213,23 @@ class GitApi(recipe_api.RecipeApi):
         str(self.package_repo_resource()), '%(PATH)s'])
 
     if use_git_cache:
-      self('retry', 'cache', 'fetch', '-c', self.m.path['git_cache'],
-           cwd=dir_path,
-           name='fetch cache',
-           can_fail_build=can_fail_build,
-           env={'PATH': path})
+      with self.m.step.context({'env': {'PATH': path}}):
+        self('retry', 'cache', 'populate', '-c', self.m.path['git_cache'], url,
+             name='populate cache',
+             can_fail_build=can_fail_build,
+             cwd=dir_path)
+        dir_cmd = self(
+            'cache', 'exists', '--quiet',
+            '--cache-dir', self.m.path['git_cache'], url,
+            can_fail_build=can_fail_build,
+            stdout=self.m.raw_io.output(),
+            step_test_data=lambda:
+                self.m.raw_io.test_api.stream_output('mirror_dir'),
+            cwd=dir_path)
+        mirror_dir = dir_cmd.stdout.strip()
+        self('remote', 'set-url', 'origin', mirror_dir,
+             can_fail_build=can_fail_build,
+             cwd=dir_path)
 
     # There are five kinds of refs we can be handed:
     # 0) None. In this case, we default to properties['branch'].

recipe_modules/git/example.expected/git-cache-checkout.json

@@ -16,15 +16,47 @@
       "git",
       "retry",
       "cache",
-      "fetch",
+      "populate",
       "-c",
-      "[GIT_CACHE]"
+      "[GIT_CACHE]",
+      "https://chromium.googlesource.com/chromium/src.git"
+    ],
+    "cwd": "[SLAVE_BUILD]/src",
+    "env": {
+      "PATH": "RECIPE_PACKAGE_REPO[depot_tools]:%(PATH)s"
+    },
+    "name": "populate cache"
+  },
+  {
+    "cmd": [
+      "git",
+      "cache",
+      "exists",
+      "--quiet",
+      "--cache-dir",
+      "[GIT_CACHE]",
+      "https://chromium.googlesource.com/chromium/src.git"
+    ],
+    "cwd": "[SLAVE_BUILD]/src",
+    "env": {
+      "PATH": "RECIPE_PACKAGE_REPO[depot_tools]:%(PATH)s"
+    },
+    "name": "git cache",
+    "stdout": "/path/to/tmp/"
+  },
+  {
+    "cmd": [
+      "git",
+      "remote",
+      "set-url",
+      "origin",
+      "mirror_dir"
     ],
     "cwd": "[SLAVE_BUILD]/src",
     "env": {
       "PATH": "RECIPE_PACKAGE_REPO[depot_tools]:%(PATH)s"
     },
-    "name": "fetch cache"
+    "name": "git remote"
   },
   {
     "cmd": [