Log HTTP errors in unit tests

Merge from Widevine repo of http://go/wvgerrit/23028

This logs the full response when the status code causes a gtest to
fail.  I hope we can figure out why the buildbot has flakey tests.

Change-Id: I498e633ad65fde4473e01ea227ffe75755fb4fd9

libwvdrmengine/cdm/core/test/cdm_engine_test.cpp

@@ -147,7 +147,8 @@ class WvCdmEngineTest : public testing::Test {
     EXPECT_TRUE(ok);
 
     int status_code = url_request.GetStatusCode(response);
-    if (expect_success) EXPECT_EQ(kHttpOk, status_code);
+    if (expect_success) EXPECT_EQ(kHttpOk, status_code)
+                            << "Error response: " << response;
 
     if (status_code != kHttpOk) {
       return "";