Experimental CompressibleString UMA

third_party/WebKit/Source/bindings/core/v8/V8StringResource.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8StringResource.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8StringResource.cpp b/third_party/WebKit/Source/bindings/core/v8/V8StringResource.cpp
index a3d51c99a7cffe26b14c255ae334807e9d4aaa9f..70149e9ac82963a895f3c9470e9f2892542fac4d 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8StringResource.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8StringResource.cpp
@@ -38,7 +38,7 @@ template<class StringClass> struct StringTraits {
 
 template<>
 struct StringTraits<String> {
-    static const String& fromStringResource(WebCoreStringResourceBase* resource)
+    static String fromStringResource(WebCoreStringResourceBase* resource)

[haraken, 2016/01/15 12:46:20]

What is this change for?

[hajimehoshi, 2016/01/18 09:42:26]

CompressibleString::string() can return an empty string: Now I found
emptyString() in WTFString.h. I'll use this.

     {
         return resource->webcoreString();
     }
@@ -48,7 +48,7 @@ struct StringTraits<String> {
 
 template<>
 struct StringTraits<AtomicString> {
-    static const AtomicString& fromStringResource(WebCoreStringResourceBase* resource)
+    static AtomicString fromStringResource(WebCoreStringResourceBase* resource)

[haraken, 2016/01/15 12:46:20]

Ditto.

[hajimehoshi, 2016/01/18 09:42:26]

Unfortunately now WebCoreStringResourceBase::atomicString can't return a
reference because AtomicString needs to be created for a CompressibleString.

     {
         return resource->atomicString();
     }
@@ -107,10 +107,17 @@ StringType v8StringToWebCoreString(v8::Local<v8::String> v8String, ExternalMode
         v8::String::ExternalStringResourceBase* resource = v8String->GetExternalStringResourceBase(&encoding);
         if (LIKELY(!!resource)) {
             WebCoreStringResourceBase* base;
-            if (encoding == v8::String::ONE_BYTE_ENCODING)
-                base = static_cast<WebCoreStringResource8*>(resource);
-            else
-                base = static_cast<WebCoreStringResource16*>(resource);
+            if (UNLIKELY(resource->IsCompressible())) {
+                if (encoding == v8::String::ONE_BYTE_ENCODING)
+                    base = static_cast<WebCoreCompressibleStringResource8*>(resource);
+                else
+                    base = static_cast<WebCoreCompressibleStringResource16*>(resource);
+            } else {
+                if (encoding == v8::String::ONE_BYTE_ENCODING)
+                    base = static_cast<WebCoreStringResource8*>(resource);
+                else
+                    base = static_cast<WebCoreStringResource16*>(resource);
+            }
             return StringTraits<StringType>::fromStringResource(base);
         }
     }