Export all CWV* symbols from the ios/web_view dynamic library.

ios/web_view/BUILD.gn

Index: ios/web_view/BUILD.gn
diff --git a/ios/web_view/BUILD.gn b/ios/web_view/BUILD.gn
index 9fe80afee29e4d326af0b112dc4a56c4561a6a71..4ca4bd207e86bb46dff340c5a17353c2fae8c096 100644
--- a/ios/web_view/BUILD.gn
+++ b/ios/web_view/BUILD.gn
@@ -19,12 +19,14 @@ ios_framework_bundle("web_view") {
 
   sources = [
     "public/cwv.h",
+    "public/cwv_export.h",

[Hiroshi Ichikawa, 2017/03/28 04:35:02]

I needed to add this here too, otherwise it causes a weird error below. Maybe we
should add all headers to "sources" as well?

$ gn gen //out/Debug-iphonesimulator --check
ERROR at //ios/web_view/public/cwv.h:14:11: Include not allowed.
#include "ios/web_view/public/cwv_export.h"
          ^-------------------------------
It is not in any dependency of
  //ios/web_view:web_view_compile_headers_map
The include file is in the target(s):
  //ios/web_view:web_view_copy_public_headers
  //ios/web_view/public:public
at least one of which should somehow be reachable.

[sdefresne, 2017/03/28 10:29:26]

public_headers are not automatically added to sources. public_headers just
inform the build systems that the headers should be copied into the generated
framework.

[michaeldo, 2017/03/28 17:34:19]

I think it's fine to only have cwv_export.h in sources. none of the other
headers are referenced so they should be fine to leave only in the
public_headers section.

   ]
 
   public_headers = [
     "public/criwv_translate_manager.h",
     "public/cwv.h",
     "public/cwv_delegate.h",
+    "public/cwv_export.h",
     "public/cwv_html_element.h",
     "public/cwv_navigation_action.h",
     "public/cwv_navigation_delegate.h",