Define a --force-gpu-rasterization flag

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 1f6209e12bb7a92394543a764d74da9ecc7c96f2..426199938a067de40fe4727822995cd34f1c0ca6 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -5535,7 +5535,8 @@ TEST_F(LayerTreeHostImplTest, MemoryPolicy) {
       gpu::MemoryAllocation::CUTOFF_ALLOW_NOTHING);
 
   // GPU rasterization should be disabled by default.
-  EXPECT_EQ(host_impl_->settings().gpu_rasterization, false);
+  EXPECT_EQ(LayerTreeSettings::CpuRasterization,
+            host_impl_->settings().rasterization_site);
 
   host_impl_->SetVisible(true);
   host_impl_->SetMemoryPolicy(policy1);
@@ -5553,7 +5554,7 @@ TEST_F(LayerTreeHostImplTest, MemoryPolicy) {
   // Now enable GPU rasterization and test if we get required only cutoff,
   // when visible.
   LayerTreeSettings settings;
-  settings.gpu_rasterization = true;
+  settings.rasterization_site = LayerTreeSettings::GpuRasterization;
   host_impl_ = LayerTreeHostImpl::Create(
       settings, this, &proxy_, &stats_instrumentation_, NULL, 0);