Re-enable GPU partial raster for non-MSAA content

cc/raster/gpu_raster_buffer_provider.cc

Index: cc/raster/gpu_raster_buffer_provider.cc
diff --git a/cc/raster/gpu_raster_buffer_provider.cc b/cc/raster/gpu_raster_buffer_provider.cc
index 86dc0105a477f3ca2ae3f9aa9ba6e6e294c8718e..f4eadee502105419071aa77d8fdf221b9cd64e9b 100644
--- a/cc/raster/gpu_raster_buffer_provider.cc
+++ b/cc/raster/gpu_raster_buffer_provider.cc
@@ -226,7 +226,10 @@ bool GpuRasterBufferProvider::IsResourceSwizzleRequired(
 }
 
 bool GpuRasterBufferProvider::CanPartialRasterIntoProvidedResource() const {
-  return false;
+  // Partial raster doesn't support MSAA, as the MSAA resolve is unaware of clip
+  // rects.
+  // TODO(crbug.com/629683): See if we can work around this limitation.
+  return msaa_sample_count_ == 0;
 }
 
 void GpuRasterBufferProvider::Shutdown() {