Increase eval compilation cache hits.

src/compilation-cache.h

Index: src/compilation-cache.h
diff --git a/src/compilation-cache.h b/src/compilation-cache.h
index 2f2fbadb2e5904cff99896bb38b7cbefb34e3d35..39420f713ebabfc7065302f02424db4db6c99851 100644
--- a/src/compilation-cache.h
+++ b/src/compilation-cache.h
@@ -126,14 +126,19 @@ class CompilationCacheScript : public CompilationSubCache {
 // considers the following pieces of information when checking for matching
 // entries:
 // 1. The source string.
-// 2. The shared function info of the calling function.
+// 2. The script of the calling function.
 // 3. Whether the source should be compiled as strict code or as non-strict
 //    code.
 //    Note: Currently there are clients of CompileEval that always compile
 //    non-strict code even if the calling function is a strict mode function.
 //    More specifically these are the CompileString, DebugEvaluate and
 //    DebugEvaluateGlobal runtime functions.
-// 4. The start position of the calling scope.
+// 4. The start position of the calling scope in the script source code.
+//    Note: The script plus the start position of the calling scope uniquely
+//    determine the shape of the outer scope of the eval call.
+//    Note: For eval calls in global context RelocInfo::kNoPosition is always
+//    used as the scope position to enable sharing between direct and indirect
+//    global eval calls.
 class CompilationCacheEval: public CompilationSubCache {
  public:
   CompilationCacheEval(Isolate* isolate, int generations)