OOP-R: GrContext::flush and glFlush at every DoEndRasterCHROMIUM

Adding egregious glFlush calls fixed this issue when GPU Raster was
going through the command buffer (in issue 863817). Adding a flush
here to see if it will fix the issue.

If this does not fix the issue, then the next steps are to
* Flush in DoRasterCHROMIUM (far more frequent) to see if that fixes
  the issue.
* Add crash instrumentation to see which commands are being issued when
  we do crash.

Bug: 906453
Change-Id: I7d88ea2d74b52751f641faaf8b848e9a1358a770
Reviewed-on: https://chromium-review.googlesource.com/c/1352508
Commit-Queue: ccameron <ccameron@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612392}

gpu/command_buffer/service/raster_decoder.cc

@@ -2516,6 +2516,19 @@ void RasterDecoderImpl::DoEndRasterCHROMIUM() {
   // prepareForExternalIO above. Use kDeferLaterCommands to ensure we yield to
   // the Scheduler before processing more commands.
   current_decoder_error_ = error::kDeferLaterCommands;
+
+#if defined(OS_MACOSX)
+  // Aggressively call glFlush on macOS to determine if this is sufficient to
+  // avoid GL driver crashes.
+  // TODO(ccameron): If this is not sufficient, then add a flush to
+  // DoRasterCHROMIUM as well. Also add crash report data to indicate which
+  // sequence of commands result in the crash, and formalize this as a GPU
+  // bug workaround.
+  // https://crbug.com/906453
+  if (gr_context())
+    gr_context()->flush();
+  api()->glFlushFn();
+#endif
 }
 
 void RasterDecoderImpl::DoCreateTransferCacheEntryINTERNAL(

gpu/command_buffer/service/raster_decoder_unittest.cc

@@ -8,6 +8,7 @@
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
+#include "build/build_config.h"
 #include "gpu/command_buffer/common/gles2_cmd_utils.h"
 #include "gpu/command_buffer/common/mailbox.h"
 #include "gpu/command_buffer/common/raster_cmd_format.h"
@@ -195,6 +196,9 @@ TEST_P(RasterDecoderManualInitTest, CopyTexSubImage2DValidateColorFormat) {
 }
 
 TEST_P(RasterDecoderTest, YieldAfterEndRasterCHROMIUM) {
+#if defined(OS_MACOSX)
+  EXPECT_CALL(*gl_, Flush()).RetiresOnSaturation();
+#endif
   GetDecoder()->SetUpForRasterCHROMIUMForTest();
   cmds::EndRasterCHROMIUM end_raster_cmd;
   end_raster_cmd.Init();