cc: Add experimental --num-raster-threads option.

Makes it possible to specify the number of worker threads used to
rasterize content.
    
BUG=154637
TEST=manual
TBR=sky@chromium.org

Review URL: https://chromiumcodereview.appspot.com/11421171

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@170655 0039d316-1c4b-4281-b951-d872f2087c98

cc/switches.cc

@@ -25,6 +25,9 @@ const char kEnablePerTilePainting[]         = "enable-per-tile-painting";
 // compositor.
 const char kEnablePinchInCompositor[]       = "enable-pinch-in-compositor";
 
+// Number of worker threads used to rasterize content.
+const char kNumRasterThreads[] = "num-raster-threads";
+
 // Show rects in the HUD around layers whose properties have changed.
 const char kShowPropertyChangedRects[] = "show-property-changed-rects";
 

cc/switches.h

@@ -22,6 +22,7 @@ CC_EXPORT extern const char kEnablePartialSwap[];
 CC_EXPORT extern const char kEnablePerTilePainting[];
 CC_EXPORT extern const char kEnablePinchInCompositor[];
 CC_EXPORT extern const char kJankInsteadOfCheckerboard[];
+CC_EXPORT extern const char kNumRasterThreads[];
 CC_EXPORT extern const char kShowPropertyChangedRects[];
 CC_EXPORT extern const char kShowSurfaceDamageRects[];
 CC_EXPORT extern const char kShowScreenSpaceRects[];

cc/tile_manager.cc

@@ -7,12 +7,15 @@
 #include <algorithm>
 
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
+#include "base/string_number_conversions.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "cc/platform_color.h"
 #include "cc/rendering_stats.h"
 #include "cc/resource_pool.h"
+#include "cc/switches.h"
 #include "cc/tile.h"
 #include "third_party/skia/include/core/SkDevice.h"
 
@@ -33,7 +36,8 @@ void RasterizeTile(cc::PicturePileImpl* picture_pile,
   picture_pile->Raster(&canvas, rect, stats);
 }
 
-const int kMaxRasterThreads = 1;
+const int kMaxRasterThreads = 64;
+const int kDefaultNumberOfRasterThreads = 1;
 
 const char* kRasterThreadNamePrefix = "CompositorRaster";
 
@@ -64,9 +68,23 @@ TileManager::TileManager(
       resource_pool_(ResourcePool::Create(resource_provider,
                                           Renderer::ImplPool)),
       manage_tiles_pending_(false),
-      pending_raster_tasks_(0),
-      worker_pool_(new base::SequencedWorkerPool(kMaxRasterThreads,
-                                                 kRasterThreadNamePrefix)) {
+      pending_raster_tasks_(0) {
+  size_t worker_threads = kDefaultNumberOfRasterThreads;
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+          cc::switches::kNumRasterThreads)) {
+    std::string num_raster_threads =
+        CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+            cc::switches::kNumRasterThreads);
+    int num_threads;
+    if (base::StringToInt(num_raster_threads, &num_threads) &&
+        num_threads > 0 && num_threads <= kMaxRasterThreads) {
+      worker_threads = num_threads;
+    } else {
+      LOG(WARNING) << "Bad number of raster threads: " << num_raster_threads;
+    }
+  }
+  worker_pool_ = new base::SequencedWorkerPool(worker_threads,
+                                               kRasterThreadNamePrefix);
 }
 
 TileManager::~TileManager() {

content/browser/renderer_host/render_process_host_impl.cc

@@ -837,6 +837,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     cc::switches::kBackgroundColorInsteadOfCheckerboard,
     cc::switches::kEnableImplSidePainting,
     cc::switches::kEnablePartialSwap,
+    cc::switches::kNumRasterThreads,
     cc::switches::kShowPropertyChangedRects,
     cc::switches::kShowSurfaceDamageRects,
     cc::switches::kShowScreenSpaceRects,