Turn on RasterInterface in the shared main thread context

This CL allows the shared main thread context to use the GLES-backed
RasterImplementationGLES raster interface. This will be a transitional
change used during the OOP-R Canvas2D project:
https://docs.google.com/document/d/1NwKi0Z-c1kQWAdKjj41283YWfLBQFegAIWnvgCvq95k
Using RasterImplementationGLES will allow us to incrementally remove
references to GLES2Interface in Canvas2D until we can use
RasterImplementation directly.

Change-Id: I189f26db8d70175908edb72050dba652d7f3df3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872932Reviewed-by: Khushal <khushalsagar@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Auto-Submit: Nathan Zabriskie <nazabris@microsoft.com>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710250}

content/renderer/render_thread_impl.cc

@@ -1424,7 +1424,7 @@ RenderThreadImpl::SharedMainThreadContextProvider() {
 
   bool support_locking = false;
   bool support_gles2_interface = true;
-  bool support_raster_interface = false;
+  bool support_raster_interface = true;
   bool support_oop_rasterization = false;
   bool support_grcontext = true;
   // Enable automatic flushes to improve canvas throughput.