Split apart the PPAPI GN targets

This puts BUILD files in the corresponding directories without duplicate names.

Adds a template for ppapi examples and writes the build for one example. I only did one at this point to test the infrastructure without making this patch too large.

NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/921953002

Cr-Commit-Position: refs/heads/master@{#316352}
diff --git a/content/browser/BUILD.gn b/content/browser/BUILD.gn
index 5196fa97..4543c90 100644
--- a/content/browser/BUILD.gn
+++ b/content/browser/BUILD.gn
@@ -248,8 +248,8 @@
                            ".",
                            "//content")
     deps += [
-      "//ppapi:ppapi_ipc",
-      "//ppapi:ppapi_shared",
+      "//ppapi/proxy:ipc",
+      "//ppapi/shared_impl",
     ]
     if (!use_ozone || use_pango) {
       sources -= [ "renderer_host/pepper/pepper_truetype_font_list_ozone.cc" ]