Add a flag for disabling Skia runtime optimizations

Skia is starting to use more advanced runtime-detected
CPU features, and this is problematic when running layout tests
(results are now machine-dependent).

Add a flag to disable Skia's runtime optimizations, and always
apply it when running layout tests.

BUG=skia:6657

Change-Id: I98e371ea60a5b0a290ba869c9134afe328ccae90
Reviewed-on: https://chromium-review.googlesource.com/512942Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#473996}

content/browser/renderer_host/render_process_host_impl.cc

@@ -1905,6 +1905,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kDisableRTCSmoothnessAlgorithm,
     switches::kDisableSeccompFilterSandbox,
     switches::kDisableSharedWorkers,
+    switches::kDisableSkiaRuntimeOpts,
     switches::kDisableSlimmingPaintInvalidation,
     switches::kDisableSmoothScrolling,
     switches::kDisableSpeechAPI,

content/public/common/content_switches.cc

@@ -279,6 +279,10 @@ const char kDisableSetuidSandbox[]          = "disable-setuid-sandbox";
 // Disable shared workers.
 const char kDisableSharedWorkers[]          = "disable-shared-workers";
 
+// Do not use runtime-detected high-end CPU optimizations in Skia.  This is
+// useful for forcing a baseline code path for e.g. layout tests.
+const char kDisableSkiaRuntimeOpts[]        = "disable-skia-runtime-opts";
+
 // Disable paint invalidation based on slimming paint.
 // See kEnableSlimmingPaintInvalidation.
 const char kDisableSlimmingPaintInvalidation[] =

content/public/common/content_switches.h

@@ -92,6 +92,7 @@ CONTENT_EXPORT extern const char kDisableResizeLock[];
 CONTENT_EXPORT extern const char kDisableSeccompFilterSandbox[];
 CONTENT_EXPORT extern const char kDisableSetuidSandbox[];
 CONTENT_EXPORT extern const char kDisableSharedWorkers[];
+CONTENT_EXPORT extern const char kDisableSkiaRuntimeOpts[];
 CONTENT_EXPORT extern const char kDisableSlimmingPaintInvalidation[];
 CONTENT_EXPORT extern const char kDisableSmoothScrolling[];
 CONTENT_EXPORT extern const char kDisableSoftwareRasterizer[];

content/renderer/renderer_main.cc

@@ -125,7 +125,11 @@ int RendererMain(const MainFunctionParams& parameters) {
   }
 #endif
 
-  SkGraphics::Init();
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDisableSkiaRuntimeOpts)) {
+    SkGraphics::Init();
+  }
+
 #if defined(OS_ANDROID)
   const int kMB = 1024 * 1024;
   size_t font_cache_limit =

content/shell/app/shell_main_delegate.cc

@@ -225,6 +225,9 @@ bool ShellMainDelegate::BasicStartupComplete(int* exit_code) {
 #endif
     }
 
+    // We want stable/baseline results when running layout tests.
+    command_line.AppendSwitch(switches::kDisableSkiaRuntimeOpts);
+
     command_line.AppendSwitch(cc::switches::kDisallowNonExactResourceReuse);
 
     // Unless/until WebM files are added to the media layout tests, we need to