Don't apply the SandboxPlugins flag until we know a plugin will be used

third_party/WebKit/Source/core/html/HTMLPlugInElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLPlugInElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLPlugInElement.cpp b/third_party/WebKit/Source/core/html/HTMLPlugInElement.cpp
index e6a69bc8e321bb99769291a911d6fb780830fb39..2ba4e25a842dcd6bc0ab0d7ac3db25d3f6dffefa 100644
--- a/third_party/WebKit/Source/core/html/HTMLPlugInElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLPlugInElement.cpp
@@ -38,6 +38,7 @@
 #include "core/html/HTMLImageLoader.h"
 #include "core/html/PluginDocument.h"
 #include "core/input/EventHandler.h"
+#include "core/inspector/ConsoleMessage.h"
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/layout/LayoutEmbeddedObject.h"
 #include "core/layout/LayoutImage.h"
@@ -474,12 +475,15 @@ bool HTMLPlugInElement::requestObject(const String& url, const String& mimeType,
         return false;
 
     KURL completedURL = url.isEmpty() ? KURL() : document().completeURL(url);
-    if (!pluginIsLoadable(completedURL, mimeType))
+    if (!objectIsLoadable(completedURL, mimeType))
         return false;
 
     bool useFallback;
-    if (shouldUsePlugin(completedURL, mimeType, hasFallbackContent(), useFallback))
+    if (shouldUsePlugin(completedURL, mimeType, hasFallbackContent(), useFallback)) {
+        if (!pluginIsLoadable(completedURL, mimeType))
+            return false;
         return loadPlugin(completedURL, mimeType, paramNames, paramValues, useFallback, true);
+    }
 
     // If the plugin element already contains a subframe,
     // loadOrRedirectSubframe will re-use it. Otherwise, it will create a new
@@ -541,8 +545,10 @@ bool HTMLPlugInElement::shouldUsePlugin(const KURL& url, const String& mimeType,
     if (document().frame()->page() && (mimeType == "image/tiff" || mimeType == "image/tif" || mimeType == "image/x-tiff")) {
         const PluginData* pluginData = document().frame()->page()->pluginData();
         String pluginName = pluginData ? pluginData->pluginNameForMimeType(mimeType) : String();
-        if (!pluginName.isEmpty() && !pluginName.contains("QuickTime", TextCaseInsensitive))
+        if (!pluginName.isEmpty() && !pluginName.contains("QuickTime", TextCaseInsensitive)) {
+            useFallback = false;
             return true;
+        }
     }
 
     ObjectContentType objectType = document().frame()->loader().client()->objectContentType(url, mimeType, shouldPreferPlugInsForImages());
@@ -561,7 +567,7 @@ void HTMLPlugInElement::dispatchErrorEvent()
         dispatchEvent(Event::create(EventTypeNames::error));
 }
 
-bool HTMLPlugInElement::pluginIsLoadable(const KURL& url, const String& mimeType)
+bool HTMLPlugInElement::objectIsLoadable(const KURL& url, const String& mimeType)
 {
     if (url.isEmpty() && mimeType.isEmpty())
         return false;
@@ -574,24 +580,35 @@ bool HTMLPlugInElement::pluginIsLoadable(const KURL& url, const String& mimeType
     if (MIMETypeRegistry::isJavaAppletMIMEType(mimeType))
         return false;
 
-    if (document().isSandboxed(SandboxPlugins))
-        return false;
-
     if (!document().securityOrigin()->canDisplay(url)) {
         FrameLoader::reportLocalLoadFailed(frame, url.string());
         return false;
     }
 
+    if (!document().contentSecurityPolicy()->allowObjectFromSource(url)) {
+        layoutEmbeddedObject()->setPluginUnavailabilityReason(LayoutEmbeddedObject::PluginBlockedByContentSecurityPolicy);
+        return false;
+    }
+
+    return (!mimeType.isEmpty() && url.isEmpty()) || !MixedContentChecker::shouldBlockFetch(frame, WebURLRequest::RequestContextObject, WebURLRequest::FrameTypeNone, url);
+}
+
+bool HTMLPlugInElement::pluginIsLoadable(const KURL& url, const String& mimeType)
+{

[pdr., 2016/02/02 04:32:42]

Can you add an assert here so future refactorings don't try calling
pluginIsLoadable by itself?
ASSERT(objectIsLoadable(url, mimetype));

[fs, 2016/02/22 18:36:56]

Done.

+    if (document().isSandboxed(SandboxPlugins)) {
+        document().addConsoleMessage(ConsoleMessage::create(SecurityMessageSource, ErrorMessageLevel,
+            "Failed to load '" + url.elidedString() + "' as a plugin, because the frame into which the plugin is loading is sandboxed."));
+        return false;
+    }
+
     AtomicString declaredMimeType = document().isPluginDocument() && document().ownerElement() ?
         document().ownerElement()->fastGetAttribute(HTMLNames::typeAttr) :
         fastGetAttribute(HTMLNames::typeAttr);
-    if (!document().contentSecurityPolicy()->allowObjectFromSource(url)
-        || !document().contentSecurityPolicy()->allowPluginTypeForDocument(document(), mimeType, declaredMimeType, url)) {
+    if (!document().contentSecurityPolicy()->allowPluginTypeForDocument(document(), mimeType, declaredMimeType, url)) {
         layoutEmbeddedObject()->setPluginUnavailabilityReason(LayoutEmbeddedObject::PluginBlockedByContentSecurityPolicy);
         return false;
     }
-
-    return (!mimeType.isEmpty() && url.isEmpty()) || !MixedContentChecker::shouldBlockFetch(frame, WebURLRequest::RequestContextObject, WebURLRequest::FrameTypeNone, url);
+    return true;
 }
 
 void HTMLPlugInElement::didAddUserAgentShadowRoot(ShadowRoot&)