[Offline Pages] Adding missing image/CSS detection in FrameSerializer.

third_party/WebKit/Source/platform/Histogram.h

Index: third_party/WebKit/Source/platform/Histogram.h
diff --git a/third_party/WebKit/Source/platform/Histogram.h b/third_party/WebKit/Source/platform/Histogram.h
index 190149eb1ecbe6d2b93984450ab958e476576866..ec4c13a22aec8f3c6ccc1edbb19f536bafbe88a4 100644
--- a/third_party/WebKit/Source/platform/Histogram.h
+++ b/third_party/WebKit/Source/platform/Histogram.h
@@ -54,6 +54,14 @@ class PLATFORM_EXPORT SparseHistogram {
   base::HistogramBase* histogram_;
 };
 
+class PLATFORM_EXPORT LinearHistogram : public CustomCountHistogram {
+ public:
+  explicit LinearHistogram(const char* name,
+                           base::HistogramBase::Sample min,
+                           base::HistogramBase::Sample max,
+                           int32_t bucket_count);
+};
+
 class PLATFORM_EXPORT ScopedUsHistogramTimer {
  public:
   ScopedUsHistogramTimer(CustomCountHistogram& counter)