Support ResourceFormat::RGBA_16F resource format for ExternalVkImage

This CL also turns on Pixel_CanvasDisplayLinearRGBAccelerated2D test

Bug: 974383
Change-Id: I6401731f3630a4a54825486eeea793ab05472266
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1834676Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702660}

content/test/gpu/gpu_tests/test_expectations/pixel_expectations.txt

@@ -178,9 +178,6 @@ crbug.com/974380 [ win ] Pixel_OffscreenCanvasUnaccelerated2DGPUCompositingWorke
 crbug.com/974380 [ mac ] Pixel_OffscreenCanvasUnaccelerated2DGPUCompositingWorker [ Skip ]
 crbug.com/974383 [ mac ] Pixel_CanvasDisplayLinearRGBAccelerated2D [ Skip ]
 
-# Also producing blank images on Intel
-crbug.com/974383 [ linux skia-renderer use-vulkan intel ] Pixel_CanvasDisplayLinearRGBAccelerated2D [ Skip ]
-
 # Fails on Intel
 crbug.com/991289 [ linux skia-renderer intel ] Pixel_CSS3DBlueBox [ Skip ]
 

gpu/command_buffer/service/external_vk_image_backing.cc

@@ -886,6 +886,11 @@ void ExternalVkImageBacking::CopyPixelsFromGLTexture() {
       gl_type = GL_UNSIGNED_INT_2_10_10_10_REV;
       bytes_per_pixel = 4;
       break;
+    case VK_FORMAT_R16G16B16A16_SFLOAT:
+      gl_format = GL_RGBA;
+      gl_type = GL_HALF_FLOAT;
+      bytes_per_pixel = 8;
+      break;
     default:
       NOTREACHED() << "Not supported resource format=" << format();
       return;
@@ -928,6 +933,8 @@ void ExternalVkImageBacking::CopyPixelsFromGLTexture() {
                      GLenum type, void* buffer) {
                     api->glReadPixelsFn(0, 0, size.width(), size.height(),
                                         format, type, buffer);
+                    DCHECK_EQ(api->glGetErrorFn(),
+                              static_cast<GLenum>(GL_NO_ERROR));
                   },
                   api, size(), gl_format, gl_type));
   api->glBindFramebufferEXTFn(GL_READ_FRAMEBUFFER, old_framebuffer);