[fsp] Add histograms for opening files.

This is a split of https://codereview.chromium.org/284443002/, to avoid
merging issues.

It is almost impossible to land a CL adding histograms via CQ, without
a merging conflict.

TBR=isherman@chromium.org
TEST=Just histograms, no actual changes.
BUG=248427

Review URL: https://codereview.chromium.org/288483002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269968 0039d316-1c4b-4281-b951-d872f2087c98

extensions/browser/extension_function_histogram_value.h

@@ -821,6 +821,8 @@ enum HistogramValue {
   FILESYSTEMPROVIDERINTERNAL_READDIRECTORYREQUESTEDSUCCESS,
   FILESYSTEMPROVIDERINTERNAL_READDIRECTORYREQUESTEDERROR,
   LEDGER_BATCHEXECUTE,
+  FILESYSTEMPROVIDERINTERNAL_OPENFILEREQUESTEDSUCCESS,
+  FILESYSTEMPROVIDERINTERNAL_OPENFILEREQUESTEDERROR,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms/histograms.xml.
   ENUM_BOUNDARY

tools/metrics/histograms/histograms.xml

@@ -34234,6 +34234,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="761"
       label="FILESYSTEMPROVIDERINTERNAL_READDIRECTORYREQUESTEDERROR"/>
   <int value="762" label="LEDGER_BATCHEXECUTE"/>
+  <int value="763" label="FILESYSTEMPROVIDERINTERNAL_OPENFILEREQUESTEDSUCCESS"/>
+  <int value="764" label="FILESYSTEMPROVIDERINTERNAL_OPENFILEREQUESTEDERROR"/>
 </enum>
 
 <enum name="ExtensionInstallCause" type="int">