Part 2.2: Is policy list subsumed under subsuming policy?

third_party/WebKit/Source/core/frame/csp/CSPSource.cpp

Index: third_party/WebKit/Source/core/frame/csp/CSPSource.cpp
diff --git a/third_party/WebKit/Source/core/frame/csp/CSPSource.cpp b/third_party/WebKit/Source/core/frame/csp/CSPSource.cpp
index 0d2dfe1a4f3665f150cde6ff3d3be7004ab91d68..a7226e42f8dfc5de4611a456fe30f2bd2a81b25e 100644
--- a/third_party/WebKit/Source/core/frame/csp/CSPSource.cpp
+++ b/third_party/WebKit/Source/core/frame/csp/CSPSource.cpp
@@ -162,6 +162,24 @@ bool CSPSource::isSchemeOnly() const {
   return m_host.isEmpty();
 }
 
+bool CSPSource::firstSubsumesSecond(HeapVector<Member<CSPSource>> a,
+                                    HeapVector<Member<CSPSource>> b) {

[Mike West, 2016/11/10 15:04:54]

Nit: `listA`, `listB`?

+  // Empty vector of CSPSources has an effect of 'none'.
+  if (a.size() == 0 || b.size() == 0)
+    return b.size() == 0;

[Mike West, 2016/11/10 15:04:54]

Nit: For all of these, you can write `a.size() == 0` as `!a.size()`. We usually
do that rather than comparing to 0.

+
+  for (const auto& bCspSrc : b) {

[Mike West, 2016/11/10 15:04:54]

Please add a comment here: something like "Walk through all the items in
|listB|, ensuring that each is subsumed by at least one item in |listA|. If any
item in |listB| is not subsumed, return false."

+    bool foundMatch = false;
+    for (const auto& aCspSrc : a) {
+      if ((foundMatch = aCspSrc->subsumes(bCspSrc)))

[Mike West, 2016/11/10 15:04:54]

Nit: `sourceA`, `sourceB`?

+        break;
+    }
+    if (!foundMatch)
+      return false;
+  }
+  return true;
+}
+
 DEFINE_TRACE(CSPSource) {
   visitor->trace(m_policy);
 }