Compile all fiddle examples locally

Motivation: it would be a good idea if the API documentation examples
were checked into the skia repository, so we could make sure they
compile as part of the commit queue.

Fiddle would make/update a named fiddle each time it gets a new
commit of Skia, extracted from the code in the examples/ directory.
The docs would point at those named fiddles.  Named fiddles have urls
in the form:

    https://fiddle.skia.org/c/@Bitmap_000

Then we would stick a link to the example into the header documentation
like this:

    /** Allocates the pixel memory for the bitmap, given its dimensions
        and SkColorType. Returns true on success, where success means
        either setPixels() or setPixelRef() was called.

        @param bitmap  SkBitmap containing SkImageInfo as input, and
                       SkPixelRef as output
        @return        true if SkPixelRef was allocated

        @example       https://fiddle.skia.org/c/@Bitmap_000
    */
    bool allocPixelRef(SkBitmap* bitmap) override;

There are still around 200 disabled examples that need to be fixed
(these result from API changes since the author left).

Change-Id: I14a31348a9ccaaa31f65424b91e3a3533d2583a7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/198824
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
diff --git a/gn/make_examples_gni.py b/gn/make_examples_gni.py
new file mode 100755
index 0000000..2fa2e97
--- /dev/null
+++ b/gn/make_examples_gni.py
@@ -0,0 +1,19 @@
+#! /usr/bin/env python
+# Copyright 2019 Google LLC.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+import glob
+import os
+head = '''# Copyright 2019 Google LLC.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+'''
+def gni(path, name, files):
+    with open(path, 'w') as o:
+        o.write('%s\n%s = get_path_info([\n' % (head, name))
+        for x in sorted(files):
+            o.write('  "%s",\n' % x)
+        o.write('], "abspath")\n')
+if __name__ == '__main__':
+    os.chdir(os.path.dirname(__file__))
+    gni('examples.gni', 'examples_sources', glob.glob('../docs/examples/*.cpp'))