[content] Disable V8 untrusted code mitigations when site isolation is enabled.

BUG=866721

Change-Id: I90a280e0d59fbc9d258e3c42a7227348b06f1ef2
Reviewed-on: https://chromium-review.googlesource.com/1150527Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579643}

content/browser/renderer_host/render_process_host_impl.cc

@@ -2716,6 +2716,11 @@ void RenderProcessHostImpl::AppendRendererCommandLine(
       child_connection_->service_token());
   command_line->AppendSwitchASCII(switches::kRendererClientId,
                                   std::to_string(GetID()));
+
+  if (SiteIsolationPolicy::UseDedicatedProcessesForAllSites()) {
+    // Disable V8 code mitigations if renderer processes are site-isolated.
+    command_line->AppendSwitch(switches::kNoV8UntrustedCodeMitigations);
+  }
 }
 
 void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(

content/public/common/content_switches.cc

@@ -624,6 +624,9 @@ const char kMojoLocalStorage[]              = "mojo-local-storage";
 // zygote to work.
 const char kNoZygote[] = "no-zygote";
 
+// Disables V8 mitigations for executing untrusted code.
+const char kNoV8UntrustedCodeMitigations[] = "no-v8-untrusted-code-mitigations";
+
 // Number of worker threads used to rasterize content.
 const char kNumRasterThreads[]              = "num-raster-threads";
 

content/public/common/content_switches.h

@@ -186,6 +186,7 @@ CONTENT_EXPORT extern const char kMHTMLSkipNostoreMain[];
 CONTENT_EXPORT extern const char kMHTMLSkipNostoreAll[];
 CONTENT_EXPORT extern const char kMojoLocalStorage[];
 CONTENT_EXPORT extern const char kNoZygote[];
+extern const char kNoV8UntrustedCodeMitigations[];
 CONTENT_EXPORT extern const char kEnableAppContainer[];
 CONTENT_EXPORT extern const char kDisableAppContainer[];
 CONTENT_EXPORT extern const char kNumRasterThreads[];

content/renderer/render_process_impl.cc

@@ -191,6 +191,12 @@ RenderProcessImpl::RenderProcessImpl(
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
 
+  if (command_line.HasSwitch(switches::kNoV8UntrustedCodeMitigations)) {
+    const char* disable_mitigations = "--no-untrusted-code-mitigations";
+    v8::V8::SetFlagsFromString(disable_mitigations,
+                               strlen(disable_mitigations));
+  }
+
   if (command_line.HasSwitch(switches::kJavaScriptFlags)) {
     std::string flags(
         command_line.GetSwitchValueASCII(switches::kJavaScriptFlags));