Enable size_t to int truncation warnings in PPAPI

Also removed a few extra "-Wpedantic" warnings in ppapi_cpp. I don't see a good justification why this should be different than the rest of the project.

Fix GN error in media.

NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/915403003

Cr-Commit-Position: refs/heads/master@{#316289}
diff --git a/ppapi/tests/test_flash_file.cc b/ppapi/tests/test_flash_file.cc
index 8e8db30..b2529404 100644
--- a/ppapi/tests/test_flash_file.cc
+++ b/ppapi/tests/test_flash_file.cc
@@ -36,7 +36,8 @@
 bool WriteFile(PP_FileHandle file_handle, const std::string& contents) {
 #if defined(PPAPI_OS_WIN)
   DWORD bytes_written = 0;
-  BOOL result = ::WriteFile(file_handle, contents.c_str(), contents.size(),
+  BOOL result = ::WriteFile(file_handle, contents.c_str(),
+                            static_cast<DWORD>(contents.size()),
                             &bytes_written, NULL);
   return result && bytes_written == static_cast<DWORD>(contents.size());
 #else