Put an arbitrary max to # of extension content scripts.

If shared memory returns bad data, then UserScriptSet might end up
allocating too much data.  This might distract crash reports to think
there was an OOM error. Set an arbitrary limit to number of scripts:
roughly 1000 extensions * 100 scripts = 100000u.

Also put |pickle_size| in crash stack to aid debugging crash reports.

Bug: 723381
Change-Id: Idf96137f5f7adec87adbacd5a276253dc5f24842
Reviewed-on: https://chromium-review.googlesource.com/570987
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486879}

extensions/renderer/user_script_set.cc

@@ -8,6 +8,7 @@
 
 #include <utility>
 
+#include "base/debug/alias.h"
 #include "base/memory/ref_counted.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/renderer/render_frame.h"
@@ -35,6 +36,11 @@ namespace {
 // user script to wrap it in an anonymous scope.
 const char kUserScriptHead[] = "(function (unsafeWindow) {\n";
 const char kUserScriptTail[] = "\n})(window);";
+// Maximum number of total content scripts we allow (across all extensions).
+// The limit exists to diagnose https://crbug.com/723381. The number is
+// arbitrarily chosen.
+// TODO(lazyboy): Remove when the bug is fixed.
+const uint32_t kNumScriptsArbitraryMax = 100000u;
 
 GURL GetDocumentUrlForFrame(blink::WebLocalFrame* frame) {
   GURL data_source_url = ScriptContext::GetDataSourceURLForFrame(frame);
@@ -115,8 +121,14 @@ bool UserScriptSet::UpdateUserScripts(base::SharedMemoryHandle shared_memory,
   base::Pickle pickle(reinterpret_cast<char*>(shared_memory_->memory()),
                       pickle_size);
   base::PickleIterator iter(pickle);
+  base::debug::Alias(&pickle_size);
   CHECK(iter.ReadUInt32(&num_scripts));
 
+  // Sometimes the shared memory contents seem to be corrupted
+  // (https://crbug.com/723381). Set an arbitrary max limit to the number of
+  // scripts so that we don't add OOM noise to crash reports.
+  CHECK_LT(num_scripts, kNumScriptsArbitraryMax);
+
   scripts_.clear();
   script_sources_.clear();
   scripts_.reserve(num_scripts);