Roll DEPS to class-dump 3.5

Removes some build warnings.

Moves the class-dump repo to a github auto-mirror instead of a mirror
that needs to be manually updated.

This also requires that the class-dump.gyp file move from the
third-party repo into the main source tree. Note that the file
structure of the class-dump source changed so the .gyp had to be
updated. For comparison, the old .class-dump.gyp can be found at
https://chromium.googlesource.com/chromium/deps/class-dump/+/master/class-dump.gyp

BUG=318160

Review URL: https://codereview.chromium.org/1106993002

Cr-Commit-Position: refs/heads/master@{#330798}

DEPS

@@ -350,7 +350,7 @@ deps_os = {
 
     # class-dump utility to generate header files for undocumented SDKs
     'src/testing/iossim/third_party/class-dump':
-     Var('chromium_git') + '/chromium/deps/class-dump.git' + '@' + '89bd40883c767584240b4dade8b74e6f57b9bdab',
+     Var('chromium_git') + '/external/github.com/nygard/class-dump.git' + '@' + '77fb7f0a2953f10501768c7551aad261fa1310b9',
 
     # Code that's not needed due to not building everything
     'src/chrome/test/data/perf/canvas_bench': None,

testing/iossim/iossim.gyp

@@ -83,7 +83,7 @@
             }],  # xcode_version
           ],  # conditions
           'dependencies': [
-            'third_party/class-dump/class-dump.gyp:class-dump#host',
+            'class-dump.gyp:class-dump#host',
           ],
           'include_dirs': [
             '<(INTERMEDIATE_DIR)/iossim',