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/Canvas_015.cpp b/docs/examples/Canvas_015.cpp
new file mode 100644
index 0000000..e40b257
--- /dev/null
+++ b/docs/examples/Canvas_015.cpp
@@ -0,0 +1,33 @@
+// 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=4486d0c0b22ad2931db130f42da4c80c
+REG_FIDDLE(Canvas_015, 256, 256, true, 0) {
+static void DeleteCallback(void*, void* context) {
+    delete (char*) context;
+}
+class CustomAllocator : public SkRasterHandleAllocator {
+public:
+    bool allocHandle(const SkImageInfo& info, Rec* rec) override {
+        char* context = new char[4]{'s', 'k', 'i', 'a'};
+        rec->fReleaseProc = DeleteCallback;
+        rec->fReleaseCtx = context;
+        rec->fHandle = context;
+        rec->fPixels = context;
+        rec->fRowBytes = 4;
+        return true;
+    }
+    void updateHandle(Handle handle, const SkMatrix& ctm, const SkIRect& clip_bounds) override {
+        // apply canvas matrix and clip to custom environment
+    }
+};
+
+void draw(SkCanvas* canvas) {
+    const SkImageInfo info = SkImageInfo::MakeN32Premul(1, 1);
+    std::unique_ptr<SkCanvas> c2 =
+            SkRasterHandleAllocator::MakeCanvas(std::unique_ptr<CustomAllocator>(
+            new CustomAllocator()), info);
+    char* context = (char*) c2->accessTopRasterHandle();
+    SkDebugf("context = %.4s\n", context);
+}
+}  // END FIDDLE