Move GrBackend enum to enum class.

Bug: skia:
Change-Id: I8add2470313549723be6720b543091c444d2eb4f
Reviewed-on: https://skia-review.googlesource.com/c/161680
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/tools/gpu/GrContextFactory.cpp b/tools/gpu/GrContextFactory.cpp
index d0ee218..d932602 100644
--- a/tools/gpu/GrContextFactory.cpp
+++ b/tools/gpu/GrContextFactory.cpp
@@ -148,9 +148,9 @@
     }
 
     std::unique_ptr<TestContext> testCtx;
-    GrBackend backend = ContextTypeBackend(type);
+    GrBackendApi backend = ContextTypeBackend(type);
     switch (backend) {
-        case kOpenGL_GrBackend: {
+        case GrBackendApi::kOpenGL: {
             GLTestContext* glShareContext = masterContext
                     ? static_cast<GLTestContext*>(masterContext->fTestContext) : nullptr;
             GLTestContext* glCtx;
@@ -202,7 +202,7 @@
             break;
         }
 #ifdef SK_VULKAN
-        case kVulkan_GrBackend: {
+        case GrBackendApi::kVulkan: {
             VkTestContext* vkSharedContext = masterContext
                     ? static_cast<VkTestContext*>(masterContext->fTestContext) : nullptr;
             SkASSERT(kVulkan_ContextType == type);
@@ -227,7 +227,7 @@
         }
 #endif
 #ifdef SK_METAL
-        case kMetal_GrBackend: {
+        case GrBackendApi::kMetal: {
             SkASSERT(!masterContext);
             testCtx.reset(CreatePlatformMtlTestContext(nullptr));
             if (!testCtx) {
@@ -236,7 +236,7 @@
             break;
         }
 #endif
-        case kMock_GrBackend: {
+        case GrBackendApi::kMock: {
             TestContext* sharedContext = masterContext ? masterContext->fTestContext : nullptr;
             SkASSERT(kMock_ContextType == type);
             if (ContextOverrides::kRequireNVPRSupport & overrides) {