Cache GL's viewport on the GPU command buffer client side.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 986dbba7e3603d696fabe1ac235414e38671b435..8c544d63d9dc435e4eb51f1e03380f32637faf01 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -3552,6 +3552,12 @@ Capabilities GLES2DecoderImpl::GetCapabilities() {
                 &caps.max_vertex_texture_image_units, 1);
   DoGetIntegerv(GL_MAX_VERTEX_UNIFORM_VECTORS, &caps.max_vertex_uniform_vectors,
                 1);
+  {
+    GLint dims[2] = {0, 0};
+    DoGetIntegerv(GL_MAX_VIEWPORT_DIMS, dims, 2);
+    caps.max_viewport_width = dims[0];
+    caps.max_viewport_height = dims[1];
+  }
   DoGetIntegerv(GL_NUM_COMPRESSED_TEXTURE_FORMATS,
                 &caps.num_compressed_texture_formats, 1);
   DoGetIntegerv(GL_NUM_SHADER_BINARY_FORMATS, &caps.num_shader_binary_formats,