Don't store webp-animated and non-webp capable image opts under same cache key.

Change the non-webp cache key to avoid picking up any that we previously messed up.
Also restructure the code a bit to lower the risk of this occuring again.

Part of issue #1216

Author: morlovich

net/instaweb/rewriter/image_rewrite_filter_test.cc

@@ -3740,4 +3740,26 @@ TEST_F(ImageRewriteTest, GifToWebpLosslessWithWebpAnimatedUa) {
                           true);
 }
 
+TEST_F(ImageRewriteTest, AnimatedNoCacheReuse) {
+  // Make sure we don't reuse results for animated webp-capable UAs for
+  // non-webp targets.
+  AddFileToMockFetcher(StrCat(kTestDomain, "a.jpeg"), kPuzzleJpgFile,
+                       kContentTypeJpeg, 100);
+
+  options()->EnableFilter(RewriteOptions::kConvertJpegToWebp);
+  options()->EnableFilter(RewriteOptions::kConvertToWebpAnimated);
+  options()->set_image_recompress_quality(85);
+  rewrite_driver()->AddFilters();
+
+  // WebP capable browser --- made a WebP image.
+  SetCurrentUserAgent("webp-animated");
+  ValidateExpected("webp broswer", "<img src=a.jpeg>",
+                   "<img src=xa.jpeg.pagespeed.ic.0.webp>");
+  ClearRewriteDriver();
+
+  // Not a WebP browser -- don't!
+  SetCurrentUserAgent("curl");
+  ValidateNoChanges("non-webp broswer", "<img src=a.jpeg>");
+}
+
 }  // namespace net_instaweb

net/instaweb/rewriter/image_url_encoder.cc

@@ -42,6 +42,10 @@ const char kMissingDimension = 'N';
 // Constants for UserAgent cache key enteries.
 const char kWebpLossyUserAgentKey[] = "w";
 const char kWebpLossyLossLessAlphaUserAgentKey[] = "v";
+const char kWebpAnimatedUserAgentKey[] = "a";
+// This used to not have a separate key, but we mixed up animated and it
+// at one point, so this is now here to force a flush.
+const char kWebpNoneUserAgentKey[] = ".";
 const char kMobileUserAgentKey[] = "m";
 const char kSmallScreenKey[] = "ss";
 
@@ -305,13 +309,19 @@ void ImageUrlEncoder::SetSmallScreen(const RewriteDriver& driver,
 GoogleString ImageUrlEncoder::CacheKeyFromResourceContext(
     const ResourceContext& resource_context) {
   GoogleString user_agent_cache_key = "";
-  if (resource_context.libwebp_level() ==
-      ResourceContext::LIBWEBP_LOSSY_LOSSLESS_ALPHA) {
-    StrAppend(&user_agent_cache_key, kWebpLossyLossLessAlphaUserAgentKey);
-  }
-  if (resource_context.libwebp_level() ==
-      ResourceContext::LIBWEBP_LOSSY_ONLY) {
-    StrAppend(&user_agent_cache_key, kWebpLossyUserAgentKey);
+  switch (resource_context.libwebp_level()) {
+    case ResourceContext::LIBWEBP_NONE:
+      StrAppend(&user_agent_cache_key, kWebpNoneUserAgentKey);
+      break;
+    case ResourceContext::LIBWEBP_LOSSY_LOSSLESS_ALPHA:
+      StrAppend(&user_agent_cache_key, kWebpLossyLossLessAlphaUserAgentKey);
+      break;
+    case ResourceContext::LIBWEBP_LOSSY_ONLY:
+      StrAppend(&user_agent_cache_key, kWebpLossyUserAgentKey);
+      break;
+    case ResourceContext::LIBWEBP_ANIMATED:
+      StrAppend(&user_agent_cache_key, kWebpAnimatedUserAgentKey);
+      break;
   }
   if (resource_context.mobile_user_agent()) {
     StrAppend(&user_agent_cache_key, kMobileUserAgentKey);

net/instaweb/rewriter/image_url_encoder_test.cc

@@ -363,7 +363,25 @@ TEST_F(ImageUrlEncoderTest, SmallScreen) {
   context.set_use_small_screen_quality(true);
   GoogleString cache_key =
       ImageUrlEncoder::CacheKeyFromResourceContext(context);
-  EXPECT_EQ("ss", cache_key);
+  EXPECT_EQ(".ss", cache_key);
+}
+
+TEST_F(ImageUrlEncoderTest, DifferentWebpLevels) {
+  // Make sure different levels of WebP support get different cache keys.
+  std::set<GoogleString> seen;
+  for (int webp_level = ResourceContext::LibWebpLevel_MIN;
+       webp_level <= ResourceContext::LibWebpLevel_MAX;
+       ++webp_level) {
+    if (ResourceContext::LibWebpLevel_IsValid(webp_level)) {
+      ResourceContext ctx;
+      ctx.set_libwebp_level(
+          static_cast<ResourceContext::LibWebpLevel>(webp_level));
+      GoogleString cache_key =
+          ImageUrlEncoder::CacheKeyFromResourceContext(ctx);
+      EXPECT_EQ(seen.find(cache_key), seen.end());
+      seen.insert(cache_key);
+    }
+  }
 }
 
 TEST_F(ImageUrlEncoderTest, BadFirst) {