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/docs/examples/Bitmap_075.cpp b/docs/examples/Bitmap_075.cpp
new file mode 100644
index 0000000..a57ffc0
--- /dev/null
+++ b/docs/examples/Bitmap_075.cpp
@@ -0,0 +1,29 @@
+// Copyright 2019 Google LLC.
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+#include "fiddle/examples.h"
+// HASH=092739b4cd5d732a27c07ced8ef45f01
+REG_FIDDLE(Bitmap_075, 256, 160, false, 0) {
+void draw(SkCanvas* canvas) {
+    auto radiusToSigma = [](SkScalar radius) -> SkScalar {
+         static const SkScalar kBLUR_SIGMA_SCALE = 0.57735f;
+         return radius > 0 ? kBLUR_SIGMA_SCALE * radius + 0.5f : 0.0f;
+    };
+    SkBitmap alpha, bitmap;
+    bitmap.allocN32Pixels(100, 100);
+    SkCanvas offscreen(bitmap);
+    offscreen.clear(0);
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setColor(SK_ColorBLUE);
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setStrokeWidth(20);
+    offscreen.drawCircle(50, 50, 39, paint);
+    offscreen.flush();
+    paint.setMaskFilter(SkMaskFilter::MakeBlur(kNormal_SkBlurStyle, radiusToSigma(25)));
+    SkIPoint offset;
+    bitmap.extractAlpha(&alpha, &paint, &offset);
+    paint.setColor(SK_ColorRED);
+    canvas->drawBitmap(bitmap, 0, -offset.fY, &paint);
+    canvas->drawBitmap(alpha, 100 + offset.fX, 0, &paint);
+}
+}  // END FIDDLE