cc: Move frame_viewer_instrumentation implementation for header to cc file

To make the reviews easier, I'm splitting up Manfred's change.
https://codereview.chromium.org/807233002/

This is a small part of his change that is separate from the rest.

Review URL: https://codereview.chromium.org/807273004

Cr-Commit-Position: refs/heads/master@{#308861}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 9aa3fde..174cb41 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -78,6 +78,7 @@
     "debug/devtools_instrumentation.h",
     "debug/frame_rate_counter.cc",
     "debug/frame_rate_counter.h",
+    "debug/frame_viewer_instrumentation.cc",
     "debug/frame_viewer_instrumentation.h",
     "debug/invalidation_benchmark.cc",
     "debug/invalidation_benchmark.h",