Add a method for dumping self-contained HTML timeline profiles

This commit adds the `--profiler-trace-path` flag. When combined with `-p` to
enable profiling, it dumps a profile as a self-contained HTML file to the given
path. The profile visualizes the traced operations as a gant-chart style
timeline.

components/profile/trace_dump.rs

@@ -0,0 +1,79 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! A module for writing time profiler traces out to a self contained HTML file.
+
+use profile_traits::time::{ProfilerCategory, TimerMetadata};
+use serde_json::{self};
+use std::fs;
+use std::io::Write;
+
+/// An RAII class for writing the HTML trace dump.
+pub struct TraceDump {
+    file: fs::File,
+}
+
+#[derive(Debug, Serialize)]
+struct TraceEntry {
+    category: ProfilerCategory,
+    metadata: Option<TimerMetadata>,
+
+    #[serde(rename = "startTime")]
+    start_time: u64,
+
+    #[serde(rename = "endTime")]
+    end_time: u64,
+
+    #[serde(rename = "startEnergy")]
+    start_energy: u64,
+
+    #[serde(rename = "endEnergy")]
+    end_energy: u64,
+}
+
+impl TraceDump {
+    /// Create a new TraceDump and write the prologue of the HTML file out to
+    /// disk.
+    pub fn new(mut file: fs::File) -> TraceDump {
+        write_prologue(&mut file);
+        TraceDump { file: file }
+    }
+
+    /// Write one trace to the trace dump file.
+    pub fn write_one(&mut self,
+                     category: &(ProfilerCategory, Option<TimerMetadata>),
+                     time: (u64, u64),
+                     energy: (u64, u64)) {
+        let entry = TraceEntry {
+            category: category.0,
+            metadata: category.1.clone(),
+            start_time: time.0,
+            end_time: time.1,
+            start_energy: energy.0,
+            end_energy: energy.1,
+        };
+        serde_json::to_writer(&mut self.file, &entry).unwrap();
+        writeln!(&mut self.file, ",").unwrap();
+    }
+}
+
+impl Drop for TraceDump {
+    /// Write the epilogue of the trace dump HTML file out to disk on
+    /// destruction.
+    fn drop(&mut self) {
+        write_epilogue(&mut self.file);
+    }
+}
+
+fn write_prologue(file: &mut fs::File) {
+    writeln!(file, "{}", include_str!("./trace-dump-prologue-1.html")).unwrap();
+    writeln!(file, "{}", include_str!("./trace-dump.css")).unwrap();
+    writeln!(file, "{}", include_str!("./trace-dump-prologue-2.html")).unwrap();
+}
+
+fn write_epilogue(file: &mut fs::File) {
+    writeln!(file, "{}", include_str!("./trace-dump-epilogue-1.html")).unwrap();
+    writeln!(file, "{}", include_str!("./trace-dump.js")).unwrap();
+    writeln!(file, "{}", include_str!("./trace-dump-epilogue-2.html")).unwrap();
+}