Remove GrContextFactory::getGLContext

Remove GrContextFactory::getGLContext, it is problematic:

It has the bug of not checking for the context type.

It also is error-prone, since the GL context is not made
current, but it is callers may assume it is current.

It is also not used very much.

Clients can use GrContextFactory::getContextInfo.

BUG=skia:

Review URL: https://codereview.chromium.org/1455093003
diff --git a/tests/GLInterfaceValidationTest.cpp b/tests/GLInterfaceValidationTest.cpp
index 7af34a7..3632c25 100755
--- a/tests/GLInterfaceValidationTest.cpp
+++ b/tests/GLInterfaceValidationTest.cpp
@@ -16,14 +16,14 @@
     for (int i = 0; i <= GrContextFactory::kLastGLContextType; ++i) {
         GrContextFactory::GLContextType glCtxType = (GrContextFactory::GLContextType)i;
         // this forces the factory to make the context if it hasn't yet
-        factory->get(glCtxType);
-        SkGLContext* glCtx = factory->getGLContext(glCtxType);
+        GrContextFactory::ContextInfo* contextInfo = factory->getContextInfo(glCtxType);
+        SkGLContext* glCtx = contextInfo->fGLContext;
 
         // We're supposed to fail the NVPR context type when we the native context that does not
         // support the NVPR extension.
         if (GrContextFactory::kNVPR_GLContextType == glCtxType &&
-            factory->getGLContext(GrContextFactory::kNative_GLContextType) &&
-            !factory->getGLContext(GrContextFactory::kNative_GLContextType)->gl()->hasExtension("GL_NV_path_rendering")) {
+            factory->getContextInfo(GrContextFactory::kNative_GLContextType) &&
+            !factory->getContextInfo(GrContextFactory::kNative_GLContextType)->fGLContext->gl()->hasExtension("GL_NV_path_rendering")) {
             REPORTER_ASSERT(reporter, nullptr == glCtx);
             continue;
         }