Run test_subdata in webgl2 mode. (#21398)

This involved improving the emulation in glTexSubImage2D.

Sadly I needed to disable this new tests in 4gb+ mode since it runs
into a chromium bug.

Author: sbc100

src/library_webgl.js

@@ -1663,6 +1663,9 @@ for (/**@suppress{duplicate}*/var i = 0; i < {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
       if (internalFormat == 0x84f9 /*GL_DEPTH_STENCIL*/) {
         internalFormat = 0x88F0 /*GL_DEPTH24_STENCIL8*/;
       }
+      if (internalFormat == 0x1908 /*GL_RGBA*/ && type == 0x1406 /*GL_FLOAT*/) {
+        internalFormat = 0x8814 /*GL_RGBA32F*/;
+      }
     }
 #endif
     if ({{{ isCurrentContextWebGL2() }}}) {

test/test_browser.py

@@ -2323,8 +2323,14 @@ def test_float_tex(self):
     self.btest('float_tex.c', reference='float_tex.png', args=['-lGL', '-lglut'])
 
   @requires_graphics_hardware
-  def test_subdata(self):
-    self.btest('gl_subdata.c', reference='float_tex.png', args=['-lGL', '-lglut'])
+  @parameterized({
+    '': ([],),
+    'es2': (['-sMIN_WEBGL_VERSION=2', '-sFULL_ES2', '-sWEBGL2_BACKWARDS_COMPATIBILITY_EMULATION'],),
+  })
+  def test_subdata(self, args):
+    if self.is_4gb() and args:
+      self.skipTest('texSubImage2D fails: https://crbug.com/325090165')
+    self.btest('gl_subdata.c', reference='float_tex.png', args=['-lGL', '-lglut'] + args)
 
   @requires_graphics_hardware
   def test_perspective(self):