Match Pepper UMA histograms by prefix

chrome/renderer/pepper/pepper_uma_host.cc

Index: chrome/renderer/pepper/pepper_uma_host.cc
diff --git a/chrome/renderer/pepper/pepper_uma_host.cc b/chrome/renderer/pepper/pepper_uma_host.cc
index 04a54296a9ba23a767c719380e6f4f3d27938190..63037c000690a8c538225f67ff8f77787a70e0c0 100644
--- a/chrome/renderer/pepper/pepper_uma_host.cc
+++ b/chrome/renderer/pepper/pepper_uma_host.cc
@@ -25,14 +25,17 @@ const char* kPredefinedAllowedUMAOrigins[] = {
   "4EB74897CB187C7633357C2FE832E0AD6A44883A"   // see crbug.com/317833
 };
 
-const char* kWhitelistedHistogramHashes[] = {
-  "F131550DAB7A7C6E6633EF81FB5998CC0482AC63",  // see crbug.com/317833
-  "13955AB4DAD798384DFB4304734FCF2A95F353CC",  // see crbug.com/317833
-  "404E800582901F1B937B8E287235FC603A5DEDFB"   // see crbug.com/317833
+// The first 12 characters must match one of the prefixes below.
+const int kWhitelistedHistogramPrefixLength = 12;

[Ilya Sherman, 2014/03/06 00:34:14]

Hmm, maybe scan up to the first dot instead?

[elijahtaylor1, 2014/03/06 00:46:27]

Great suggestion.  Done.

+
+const char* kWhitelistedHistogramPrefixes[] = {

[Ilya Sherman, 2014/03/06 00:34:14]

nit: "const char* const"

[elijahtaylor1, 2014/03/06 00:46:27]

Done.

+  "CD190EA2B764EDF0BB97552A638D32072F3CFD41",  // see crbug.com/317833

[Ilya Sherman, 2014/03/06 00:34:14]

nit: Links should start with "http://".  Also, this is a restricted bug, which
might frustrate some folks trying to understand the code... but maybe that's the
best we can do in this case?

[elijahtaylor1, 2014/03/06 00:46:27]

Fixed "http://"

Yeah, I agree that could be frustrating, but the alternative right now is no bug
link to explain it, which would frustrate all folks.

 };
 
-std::string HashHistogram(const std::string& histogram) {
-  const std::string id_hash = base::SHA1HashString(histogram);
+
+std::string HashPrefix(const std::string& histogram) {
+  const std::string id_hash = base::SHA1HashString(
+      histogram.substr(0, kWhitelistedHistogramPrefixLength));
   DCHECK_EQ(id_hash.length(), base::kSHA1Length);
   return base::HexEncode(id_hash.c_str(), id_hash.length());
 }
@@ -48,8 +51,8 @@ PepperUMAHost::PepperUMAHost(
       is_plugin_in_process_(host->IsRunningInProcess()) {
   for (size_t i = 0; i < arraysize(kPredefinedAllowedUMAOrigins); ++i)
     allowed_origins_.insert(kPredefinedAllowedUMAOrigins[i]);
-  for (size_t i = 0; i < arraysize(kWhitelistedHistogramHashes); ++i)
-    allowed_histograms_.insert(kWhitelistedHistogramHashes[i]);
+  for (size_t i = 0; i < arraysize(kWhitelistedHistogramPrefixes); ++i)
+    allowed_histogram_prefixes_.insert(kWhitelistedHistogramPrefixes[i]);
 }
 
 PepperUMAHost::~PepperUMAHost() {
@@ -78,8 +81,8 @@ bool PepperUMAHost::IsHistogramAllowed(const std::string& histogram) {
       ChromeContentRendererClient::IsExtensionOrSharedModuleWhitelisted(
           document_url_, allowed_origins_);
   if (is_whitelisted &&
-      allowed_histograms_.find(HashHistogram(histogram)) !=
-          allowed_histograms_.end()) {
+      allowed_histogram_prefixes_.find(HashPrefix(histogram)) !=
+          allowed_histogram_prefixes_.end()) {
     return true;
   }