Add a flag to disable partial raster in renderer

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 8b96d45745bd90c5ec1a0613fa09173ec28c4b8d..4c5cc189e6ac876c81b9bd6524c8c49e8832e39f 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -1138,13 +1138,16 @@ static void AppendCompositorCommandLineFlags(base::CommandLine* command_line) {
 
   if (IsZeroCopyUploadEnabled())
     command_line->AppendSwitch(switches::kEnableZeroCopy);
-  if (IsPersistentGpuMemoryBufferEnabled())
-    command_line->AppendSwitch(switches::kEnablePersistentGpuMemoryBuffer);
+  if (IsPartialRasterEnabled())
+    command_line->AppendSwitch(switches::kEnablePartialRaster);
 
   if (IsForceGpuRasterizationEnabled())
     command_line->AppendSwitch(switches::kForceGpuRasterization);
 
-  gfx::BufferUsage buffer_usage = IsPersistentGpuMemoryBufferEnabled()
+  // Persistent buffers may come at a performance hit (not all platform specific
+  // buffers support it), so only enable them if partial raster is enabled and
+  // we are actually going to use them.
+  gfx::BufferUsage buffer_usage = IsPartialRasterEnabled()
                                       ? gfx::BufferUsage::PERSISTENT_MAP
                                       : gfx::BufferUsage::MAP;
   std::vector<unsigned> image_targets(