Copy some PlaybackToStagingBuffer state to the stack and alias it.

Temporarily add some values to minidumps, to help diagnose crash
reports under SkDraw::drawPaint and related signatures.

Bug: 870663
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I84f3aed1c50c8e44bc882e6655688bd26c0e4edc
Reviewed-on: https://chromium-review.googlesource.com/1196226Reviewed-by: Khushal <khushalsagar@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587781}

cc/raster/one_copy_raster_buffer_provider.cc

@@ -10,6 +10,7 @@
 #include <limits>
 #include <utility>
 
+#include "base/debug/alias.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/trace_event/process_memory_dump.h"
@@ -355,6 +356,17 @@ void OneCopyRasterBufferProvider::PlaybackToStagingBuffer(
     // RasterBufferProvider::PlaybackToMemory only supports unsigned strides.
     DCHECK_GE(buffer->stride(0), 0);
 
+    // TODO(https://crbug.com/870663): Temporary diagnostics.
+    base::debug::Alias(&playback_rect);
+    base::debug::Alias(&full_rect_size);
+    base::debug::Alias(&rv);
+    void* buffer_memory = buffer->memory(0);
+    base::debug::Alias(&buffer_memory);
+    gfx::Size staging_buffer_size = staging_buffer->size;
+    base::debug::Alias(&staging_buffer_size);
+    gfx::Size buffer_size = buffer->GetSize();
+    base::debug::Alias(&buffer_size);
+
     DCHECK(!playback_rect.IsEmpty())
         << "Why are we rastering a tile that's not dirty?";
     RasterBufferProvider::PlaybackToMemory(