Reland "content: Copy plugin code from Blink to Chromium."

This relands r245843, which was reverted because it broke check_licenses
on Android Build. This time it was added the chromium copyright
boilerplate to files that had Apple copyright and replaced Google
copyright with Chromium one.

BUG=331302
TEST=None
R=boliu@chromium.org, jochen@chromium.org

Review URL: https://codereview.chromium.org/143373003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245954 0039d316-1c4b-4281-b951-d872f2087c98

android_webview/tools/webview_licenses.py

@@ -107,6 +107,8 @@ def _CheckLicenseHeaders(excluded_dirs_list, whitelisted_files):
   excluded_dirs_list.append('chrome/tools/test/reference_build')
   # blink style copy right headers.
   excluded_dirs_list.append('content/shell/renderer/test_runner')
+  # blink style copy right headers.
+  excluded_dirs_list.append('content/shell/tools/plugin')
   # This is tests directory, doesn't exist in the snapshot
   excluded_dirs_list.append('content/test/data')
   # This is a tests directory that doesn't exist in the shipped product.