Use layout test support flag to turn on single thread compositor proxy scheduler

Mainly to remove dependency from test runner on content

BUG=478250
R=enne@chromium.org

Review URL: https://codereview.chromium.org/1129683003

Cr-Commit-Position: refs/heads/master@{#329756}

content/public/common/content_switches.cc

@@ -232,10 +232,6 @@ const char kDisableSetuidSandbox[]          = "disable-setuid-sandbox";
 // Disable shared workers.
 const char kDisableSharedWorkers[]          = "disable-shared-workers";
 
-// For tests, disable single thread scheduler and only manually composite.
-const char kDisableSingleThreadProxyScheduler[] =
-    "disable-single-thread-proxy-scheduler";
-
 // Disable smooth scrolling for testing.
 const char kDisableSmoothScrolling[]        = "disable-smooth-scrolling";
 

content/public/common/content_switches.h

@@ -78,7 +78,6 @@ extern const char kDisableRendererAccessibility[];
 CONTENT_EXPORT extern const char kDisableSeccompFilterSandbox[];
 CONTENT_EXPORT extern const char kDisableSetuidSandbox[];
 CONTENT_EXPORT extern const char kDisableSharedWorkers[];
-CONTENT_EXPORT extern const char kDisableSingleThreadProxyScheduler[];
 CONTENT_EXPORT extern const char kDisableSmoothScrolling[];
 CONTENT_EXPORT extern const char kDisableSoftwareRasterizer[];
 CONTENT_EXPORT extern const char kDisableSpeechAPI[];

content/renderer/render_thread_impl.cc

@@ -1415,8 +1415,9 @@ bool RenderThreadImpl::IsElasticOverscrollEnabled() {
 }
 
 bool RenderThreadImpl::UseSingleThreadScheduler() {
-  base::CommandLine* cmd = base::CommandLine::ForCurrentProcess();
-  return !cmd->HasSwitch(switches::kDisableSingleThreadProxyScheduler);
+  // TODO(enne): using the scheduler introduces additional composite steps
+  // that create flakiness.  This should go away eventually.
+  return !layout_test_mode_;
 }
 
 uint32 RenderThreadImpl::GetImageTextureTarget() {

content/shell/renderer/test_runner/web_test_proxy.cc

@@ -13,7 +13,6 @@
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/trace_event/trace_event.h"
-#include "content/public/common/content_switches.h"
 #include "content/shell/renderer/test_runner/accessibility_controller.h"
 #include "content/shell/renderer/test_runner/event_sender.h"
 #include "content/shell/renderer/test_runner/mock_color_chooser.h"
@@ -390,10 +389,6 @@ WebTestProxyBase::WebTestProxyBase()
       web_widget_(NULL),
       spellcheck_(new SpellCheckClient(this)),
       chooser_count_(0) {
-  // TODO(enne): using the scheduler introduces additional composite steps
-  // that create flakiness.  This should go away eventually.
-  base::CommandLine::ForCurrentProcess()->AppendSwitch(
-      switches::kDisableSingleThreadProxyScheduler);
   Reset();
 }