Move policy generated files to components/policy

Previously these were generated in a "policy" toplevel directory. Generally
components should use the GN target_gen_dir for the generated files for
consistency.

policy_proto_export.h was moved to the proto directory. DEPS files were updated
(a few rules were broadened to all of components/policy since listing
individual headers in DEPS is not helpful and makes it more difficult for
others down the road).

The rest of the changes are mechanical search-and-replace for the new paths.

TBR=dbeam for chrome/browser/ui/webui

Review-Url: https://codereview.chromium.org/2273783002
Cr-Commit-Position: refs/heads/master@{#414094}
diff --git a/chrome/browser/extensions/policy_handlers_unittest.cc b/chrome/browser/extensions/policy_handlers_unittest.cc
index 324b8a3..1a0f91883 100644
--- a/chrome/browser/extensions/policy_handlers_unittest.cc
+++ b/chrome/browser/extensions/policy_handlers_unittest.cc
@@ -11,9 +11,9 @@
 #include "components/policy/core/common/policy_map.h"
 #include "components/policy/core/common/policy_types.h"
 #include "components/policy/core/common/schema.h"
+#include "components/policy/policy_constants.h"
 #include "components/prefs/pref_value_map.h"
 #include "extensions/browser/pref_names.h"
-#include "policy/policy_constants.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace extensions {