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/Pixmap_020.cpp b/docs/examples/Pixmap_020.cpp
new file mode 100644
index 0000000..1d795f5
--- /dev/null
+++ b/docs/examples/Pixmap_020.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=94ad244056dc80ecd87daae004266334
+REG_FIDDLE(Pixmap_020, 256, 256, true, 0) {
+void draw(SkCanvas* canvas) {
+    const int w = 4;
+    const int h = 4;
+    std::vector<SkPMColor> storage;
+    storage.resize(w * h);
+    SkDebugf("Premultiplied:\n");
+    for (int y = 0; y < h; ++y) {
+        SkDebugf("(0, %d) ", y);
+        for (int x = 0; x < w; ++x) {
+            int a = 0xFF * (x + y) / (w - 1 + h - 1);
+            storage[x + y * w] = SkPackARGB32(a, a * x / (w - 1), a * y / (h - 1), a);
+            SkDebugf("0x%08x%c", storage[x + y * w], x == w - 1 ? '\n' : ' ');
+        }
+    }
+    SkPixmap pixmap(SkImageInfo::MakeN32(w, h, kPremul_SkAlphaType), &storage.front(), w * 4);
+    SkDebugf("Unpremultiplied:\n");
+    for (int y = 0; y < h; ++y) {
+        SkDebugf("(0, %d) ", y);
+        for (int x = 0; x < w; ++x) {
+            SkDebugf("0x%08x%c", pixmap.getColor(x, y), x == w - 1 ? '\n' : ' ');
+        }
+    }
+}
+}  // END FIDDLE