Require size_bytes for first class GCS dep

GCS deps will require a size_bytes field of type `int`. If gclient
sees that the actual byte size is different than the noted size, it
will raise an exception.

Bug: b/328065441
Change-Id: If61496eae39cd372966d7e64ba4a84759708c60b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5367540
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Stephanie Kim <kimstephanie@google.com>

testing_support/fake_repos.py

@@ -896,12 +896,14 @@ deps = {
             'object_name': 'deadbeef',
             'dep_type': 'gcs',
             'sha256sum': 'abcd123',
+            'size_bytes': 10000,
           },
           'src/another_gcs_dep': {
             'bucket': '456bucket',
             'object_name': 'Linux/llvmfile.tar.gz',
             'dep_type': 'gcs',
             'sha256sum': 'abcd123',
+            'size_bytes': 10000,
           },
           'src/gcs_dep_with_output_file': {
             'bucket': '789bucket',
@@ -909,6 +911,7 @@ deps = {
             'dep_type': 'gcs',
             'sha256sum': 'abcd123',
             'output_file': 'clang-format-no-extract',
+            'size_bytes': 10000,
           },
         }"""),
                 'origin':
@@ -943,6 +946,7 @@ deps = {
     'object_name': 'path_to_file.tar.gz',
     'dep_type': 'gcs',
     'sha256sum': 'abcd123',
+    'size_bytes': 10000,
   },
 }
 """,