PDF: Add UMA to track embedded PDF triggered drive-by downloads.

chrome/common/BUILD.gn

Index: chrome/common/BUILD.gn
diff --git a/chrome/common/BUILD.gn b/chrome/common/BUILD.gn
index 6d49fa125baae79142b387ed06df1bf27e03fdfc..8922e36c8db0a6bfdea108b483b7954a18b9b4e7 100644
--- a/chrome/common/BUILD.gn
+++ b/chrome/common/BUILD.gn
@@ -469,6 +469,12 @@ static_library("common") {
     ]
   }
 
+  if (enable_pdf) {

[Lei Zhang, 2017/05/24 22:39:21]

You are using BUILDFLAG(ENABLE_PLUGINS) in the C++ code. Is that the same as
enable_pdf?

[tommycli, 2017/05/25 18:16:37]

Actually i have no idea what i was thinking. i specifically want this enabled
whether or not there's PDF or plugins.

+    sources += [
+      "pdf_uma.cc",
+      "pdf_uma.h",
+    ]
+  }
   if (enable_plugins) {
     sources += [
       "pepper_flash.cc",