Implement support for using GL ES 3.0 with command buffer

Adds a new 'api': --config gpu(api=commandbuffer3) for dm/nanobench.

BUG=skia:4943
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1684413003

Review URL: https://codereview.chromium.org/1684413003
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 7ebac5f..5b13310 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -206,9 +206,9 @@
                 break;
 #endif // SK_ANGLE
 #if SK_COMMAND_BUFFER
-            case kCommandBuffer_DeviceType:
+            case kCommandBufferES2_DeviceType:
                 // Command buffer is really the only other odd man out :D
-                fBackend = kCommandBuffer_BackEndType;
+                fBackend = kCommandBufferES2_BackEndType;
                 break;
 #endif // SK_COMMAND_BUFFER
             default:
@@ -237,7 +237,7 @@
                 break;
 #endif // SK_ANGLE
 #if SK_COMMAND_BUFFER
-            case kCommandBuffer_DeviceType:
+            case kCommandBufferES2_DeviceType:
                 glInterface.reset(GrGLCreateCommandBufferInterface());
                 break;
 #endif // SK_COMMAND_BUFFER
@@ -692,7 +692,7 @@
         , SampleWindow::kANGLE_DeviceType
 #endif // SK_ANGLE
 #if SK_COMMAND_BUFFER
-        , SampleWindow::kCommandBuffer_DeviceType
+        , SampleWindow::kCommandBufferES2_DeviceType
 #endif // SK_COMMAND_BUFFER
 #endif // SK_SUPPORT_GPU
     };
@@ -859,7 +859,7 @@
     fDeviceType = kANGLE_DeviceType;
 #endif
 #if SK_COMMAND_BUFFER && DEFAULT_TO_COMMAND_BUFFER
-    fDeviceType = kCommandBuffer_DeviceType;
+    fDeviceType = kCommandBufferES2_DeviceType;
 #endif
 
     fUseClip = false;