Add flag to Viewer to trigger continuous redraw.

Change-Id: I71059001567b39afc486a2f099efdffde42b0d1b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254681
Auto-Submit: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index f02f5b9..ec9d523 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -129,6 +129,8 @@
                "Run threadsafe tests on a threadpool with this many extra threads, "
                "defaulting to one extra thread per core.");
 
+static DEFINE_bool(redraw, false, "Toggle continuous redraw.");
+
 
 const char* kBackendTypeStrings[sk_app::Window::kBackendTypeCount] = {
     "OpenGL",
@@ -311,6 +313,7 @@
     displayParams.fGrContextOptions.fSuppressPrints = true;
     displayParams.fGrContextOptions.fInternalMultisampleCount = FLAGS_internalSamples;
     fWindow->setRequestedDisplayParams(displayParams);
+    fRefresh = FLAGS_redraw;
 
     // Configure timers
     fStatsLayer.setActive(false);