Include necessary base/ headers in raster_source.h.

Include what you use. Also forward declare another base/ class that is
referenced in the header.

Change-Id: I0218c5acc0fe22b61eb5df9b41f475f1c103bcad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2858117
Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#877542}

cc/raster/raster_source.h

@@ -10,6 +10,8 @@
 #include <memory>
 #include <vector>
 
+#include "base/containers/flat_map.h"
+#include "base/memory/ref_counted.h"
 #include "cc/cc_export.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/layers/recording_source.h"
@@ -18,6 +20,12 @@
 #include "third_party/skia/include/core/SkPicture.h"
 #include "ui/gfx/color_space.h"
 
+namespace base {
+namespace trace_event {
+class TracedValue;
+}  // namespace trace_event
+}  // namespace base
+
 namespace gfx {
 class AxisTransform2d;
 }  // namespace gfx