Add ShaderErrorHandler to GrContextOptions

Allows clients to customize behavior when shaders fail to compile.
Added nicer shader error handling to viewer.

Change-Id: If82b48e40d64fd786f37e88c564fd623b53c7f9d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/211361
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index ca9e679..98d6f21 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -21,6 +21,7 @@
 #include "src/gpu/GrResourceCache.h"
 #include "src/gpu/GrResourceProvider.h"
 #include "src/gpu/GrSemaphore.h"
+#include "src/gpu/GrShaderUtils.h"
 #include "src/gpu/GrSoftwarePathRenderer.h"
 #include "src/gpu/GrTracing.h"
 #include "src/gpu/SkGr.h"
@@ -92,6 +93,10 @@
     }
 
     fPersistentCache = this->options().fPersistentCache;
+    fShaderErrorHandler = this->options().fShaderErrorHandler;
+    if (!fShaderErrorHandler) {
+        fShaderErrorHandler = GrShaderUtils::DefaultShaderErrorHandler();
+    }
 
     return true;
 }