Allow startup with missing V8 snapshot file.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 0e7f4d2ed9837d8b52ca42ab7487695075620fac..15df5051fc00ded334fc9a74bb94444c29d2987c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -45047,6 +45047,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Time spent in scavenging phase of GC.</summary>
 </histogram>
 
+<histogram name="V8.Initializer.LoadV8Natives.Result"
+    enum="V8InitializerLoadV8NativesResult">
+  <owner>oth@chromium.org</owner>
+  <summary>Results from natives loading.</summary>
+</histogram>

[rmcilroy, 2015/06/01 14:06:31]

According to Orion the current UMA didn't show much since crashes prevent the
UMA from being sent. I guess we would like to keep UMA for the snapshot loading
to check how often it doesn't find the snapshot, but we probably don't need to
add the natives UMA, WDYT?

[Erik Corry Chromium.org, 2015/06/02 11:18:53]

Sounds right

+
 <histogram name="V8.Initializer.LoadV8Snapshot.Result"
     enum="V8InitializerLoadV8SnapshotResult">
   <owner>oth@chromium.org</owner>
@@ -66394,6 +66400,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="6" label="CHECKSUM_MISMATCH">Reject due to checksum mismatch</int>
 </enum>
 
+<enum name="V8InitializerLoadV8NativesResult" type="int">
+  <int value="0" label="SUCCESS">Load succeeded</int>
+  <int value="1" label="FAILED_OPEN">Failure to open natives file</int>
+  <int value="2" label="FAILED_MAP">Failed to map natives</int>
+  <int value="3" label="FAILED_VERIFY">Failed to verify natives</int>
+</enum>
+
 <enum name="V8InitializerLoadV8SnapshotResult" type="int">
   <int value="0" label="SUCCESS">Load succeeded</int>
   <int value="1" label="FAILED_OPEN">Failure to open snapshot file</int>